Zymborski Projection System (ZiPS)

ZiPS is a system of player projections developed by FanGraph's Dan Szymborski when he was at Baseball Think Factory. According a Q&A on the Baseball Think Factory website, ZiPS uses growth and decline curves based on player type to find trends. It then factors those trends into the past performance of those players to come up with projections.

Win (W)

A pitcher receives a win when he is the pitcher of record when his team takes the lead for good -- with a couple rare exceptions. First, a starting pitcher must pitch at least five innings (in a traditional game of nine innings or longer) to qualify for the win. If he does not, the official scorer awards the win to the most effective relief pitcher.

Wins Above Replacement (WAR)

WAR measures a player's value in all facets of the game by deciphering how many more wins he's worth than a replacement-level player at his same position (e.g., a Minor League replacement or a readily available fill-in free agent).

Win Probability Added (WPA)

WPA quantifies the percent change in a team's chances of winning from one event to the next. It does so by measuring the importance of a given plate appearance in the context of the game. For instance: a homer in a one-run game is worth more than a homer in a blowout.

Winning Percentage (WPCT)

A pitcher's winning percentage is calculated by dividing his total number of wins by his total number of decisions (wins plus losses). Pitchers who get the win or the loss are known as the "pitchers of record" in a game, and winning percentage indicates how frequently a pitcher wins when he is the pitcher of record.

Win Expectancy (WE)

Win Expectancy (WE), otherwise known as Win Probability, indicates the chance a team has to win a particular game at a specific point in that game.

Windup Position

Pitchers are permitted to use two legal pitching deliveries -- the windup position and the set position -- and either position may be used at any time.

Wild Pitch (WP)

A pitcher is charged with a wild pitch when his pitch is so errant that the catcher is unable to control it and, as a result, baserunner(s) advance. (This is an important stipulation. No matter how poor the pitch, a pitcher is only charged with a WP if at least one runner moves up a base, and he cannot be charged with a wild pitch if no one is on base -- unless it allows the batter to reach base on a third strike.)

Weighted Runs Created Plus (wRC+)

wRC+ takes the statistic Runs Created and adjusts that number to account for important external factors -- like ballpark or era. It's adjusted, so a wRC+ of 100 is league average and 150 would be 50 percent above league average.

Weighted Runs Above Average (wRAA)

wRAA measures how many runs a hitter contributes, compared with an average player -- so a player with a 0 wRAA would be considered league average, offensively. It's calculated by finding the difference in the number of runs contributed between a player and the league average (which is determined by the league average wOBA).

Weighted On-base Average (wOBA)

wOBA is a version of on-base percentage that accounts for how a player reached base -- instead of simply considering whether a player reached base. The value for each method of reaching base is determined by how much that event is worth in relation to projected runs scored (example: a double is worth more than a single).

Warmup Pitches

When taking their position at the beginning of an inning or when relieving another pitcher, pitchers are permitted to throw as many warmup pitches as they want within the countdown parameters set forth by Major League Baseball.

Walks Per Nine Innings (BB/9)

Walks per nine innings tells us how many walks a given pitcher allows per nine innings pitched -- using the formula walks divided by innings times nine.

Walks And Hits Per Inning Pitched (WHIP)

WHIP is one of the most commonly used statistics for evaluating a pitcher's performance. The statistic shows how well a pitcher has kept runners off the basepaths, one of his main goals. The formula is simple enough -- it's the sum of a pitcher's walks and hits, divided by his total innings pitched.

Walk Rate (BB%)

Walk rate represents the frequency with which a pitcher walks hitters, as determined by total walks divided by total batters faced. It's an important tool for assessing a pitcher's capabilities and perhaps the most important in judging a pitcher's tendency to walk batters.

Walk-off (WO)

A walk-off occurs when the home team takes the lead in the bottom of the ninth or extra innings. Because the visiting team will not get another turn at-bat, the game ends immediately, with the home team victorious.


A "walk-off" is any offensive play that gives the home team the lead -- and thus, the win -- in the bottom of the last inning.

Walk (BB)

A walk (or base on balls) occurs when a pitcher throws four pitches out of the strike zone, none of which are swung at by the hitter. After refraining from swinging at four pitches out of the zone, the batter is awarded first base. In the scorebook, a walk is denoted by the letters BB.

Vesting Option

A vesting option is an optional year at the end of the contract that becomes guaranteed if the player reaches a certain performance incentive threshold. Vesting options are typically based on playing time incentives such as plate appearances, innings pitched, games started or games finished. In most cases, a vesting option that fails to vest can still be exercised as a club option.

Velocity (VELO)

Velocity, one of the most frequently used tools for evaluating pitchers, represents the maximum speed of a given pitch at any point from its release to the time it crosses home plate.

Unearned Run (UER)

An unearned run is any run that scored because of an error or a passed ball. Oftentimes, it is the judgment of the official scorer as to whether a specific run would've scored without the defensive mishap.


Umpires are responsible for enforcing on-field rules and rendering decisions on judgment calls such as: Whether a batter or baserunner is safe or out, and whether a pitched baseball is a strike or a ball.

Ultimate Zone Rating (UZR)

UZR quantifies a player's entire defensive performance by attempting to measure how many runs a defender saved. It takes into account errors, range, outfield arm and double-play ability. It differs slightly from DRS (Defensive Runs Saved) in its formula, but the concept is the same.

Two-way Players

Prior to the 2020 season, Major League Baseball instituted a rule requiring all MLB teams to designate every player on the active roster as either a pitcher or a position player. Those designated as position players would have been unable to pitch unless it was extra innings, their team was ahead or trailing by more than six runs, or they had qualified as a two-way player.

Two-Seam Fastball (FT)

A two-seam fastball is generally one of a pitcher's fastest pitches, although it doesn't have quite the same velocity as a four-seam fastball. A two-seam fastball is one of the most frequently thrown pitches in baseball.

Triple Play (TP)

A triple play occurs when the defending team records three outs on a single defensive play.

Triple (3B)

Often called "the most exciting play in baseball," a triple occurs when a batter hits the ball into play and reaches third base without the help of an intervening error or attempt to put out another baserunner.

Trade Waivers & Aug. 31 'Deadline'

In a typical season, the Trade Deadline almost always falls on July 31. Players may still be placed and claimed on outright waivers after July 31, but trades aren't permitted after that date.

Trade Deadline

In a typical season, the Trade Deadline almost always* falls at 4 p.m. ET on July 31 and is the last point during the regular season at which players can be traded from one club to another.

Total Chances (TC)

In theory, a defender's total chances represent the number of opportunities he has to record an out. The formula for total chances is: assists plus putouts plus errors.

Total Bases (TB)

Total bases refer to the number of bases gained by a batter through his hits. A batter records one total base for a single, two total bases for a double, three total bases for a triple and four total bases for a home run.


TOOTBLAN is an acronym that stands for Thrown Out on the Bases Like a Nincompoop.

Tools of Ignorance

"Tools of ignorance" is a nickname for the catcher's equipment.

Tommy John Surgery

Tommy John surgery is a procedure in which a partial or fully torn ulnar collateral ligament on the medial side of the elbow is replaced with a tendon from another part of a patient's body or from a cadaver.

Three True Outcomes

The "three true outcomes" in baseball are said to be a home run, a walk or a strikeout due to the fact that none of the three, with the rare exception of an inside-the-park home run or a strikeout with a dropped third strike, involve the defense beyond the pitcher or the catcher. The phrase, which was coined by baseball writer and historian Christina Kahrl, can also be used as an adjective, calling someone a "three-true-outcomes player." Players with well above-average power, walk rates and strikeout tendencies often bear that description.

Three-batter Minimum

In an effort to reduce the number of pitching changes and, in turn, cut down the average time per game, MLB instituted a rule change that requires pitchers to either face a minimum of three batters in an appearance or pitch to the end of a half-inning, with exceptions for injuries and illnesses. If a pitcher faces one batter to end an inning, he may be removed, but if he is brought back for a second inning, he must still face two more batters for a total of three.

Thoracic Outlet Syndrome

The thoracic outlet lies at the lower part of the neck, beginning just above and behind the collarbone and extending into the upper arm and chest. Thoracic Outlet Syndrome results when the nerves and blood vessels in this area are compressed, resulting in pain, weakness, fatigue and numbness or tingling in the arm or hand, particularly with activities in which the arm is elevated.

Third Baseman

The third baseman positions himself in the vicinity of the third-base bag, facing home plate with the base in front of him and to the right.

Third-base Coach

The third-base coach stands in foul ground, just behind the third-base bag, and helps relay signals from the dugout to both batters and baserunners. With a batter at the plate, a third-base coach will use pre-determined hand and arm gestures to indicate when said batter is expected to bunt, execute a "hit-and-run," or "take a pitch." By rule, the third-base coach must stay within the designated coach's box on the third-base side of home plate prior to each pitch. The coach may leave said box to signal a player once a ball is in play, provided the coach does not interfere with the play.

The Hot Stove

"The Hot Stove" refers to the Major League Baseball offseason, particularly the time around the Winter Meetings when free-agent signings and trades are most prevalent.

Texas Leaguer

A "Texas Leaguer" is a bloop that falls between an outfielder and an infielder for a hit.

Sweet Spot

Colloquially, a player who hits the ball solidly is said to have gotten the "sweet spot" of the bat on the ball. The sweet spot classification quantifies that as a batted-ball event with a launch angle ranging from 8 to 32 degrees.

Suspended Game

A suspended game is a game that is stopped early and must be completed at a later date from the point of termination, though not all terminated games become suspended games.

Super Two

Players typically must accrue three years of Major League service time -- with one year of service time equaling 172 days on the 25-man roster or the Major League injured list -- to become eligible for salary arbitration. Super Two is a designation that allows a select group of players to become eligible for arbitration before reaching three years of service time.


Teams are permitted to substitute players any time the ball is dead. The manager must immediately notify the umpire of the switch and substitutes must bat in the replaced player's batting-order position. Once removed, players are not permitted to return to the game in any capacity. Types of substitutions include pinch-hitting, pinch-running, a pitching change and a defensive replacement.

Strike Zone

The official strike zone is the area over home plate from the midpoint between a batter's shoulders and the top of the uniform pants -- when the batter is in his stance and prepared to swing at a pitched ball -- and a point just below the kneecap. In order to get a strike call, part of the ball must cross over part of home plate while in the aforementioned area.

Strikeout-to-walk Ratio (K/BB)

K/BB ratio tells us how many strikeouts a pitcher records for each walk he allows. The number is found simply by dividing a pitcher's total number of strikeouts by his total number of walks. It's an essential tool for evaluating pitchers.

Strikeouts Per Nine Innings (K/9)

K/9 rate measures how many strikeouts a pitcher averages for every nine innings pitched. It is determined by dividing his strikeout total by his innings pitched total and multiplying the result by nine.

Strikeout (SO, K)

A strikeout occurs when a pitcher throws any combination of three swinging or looking strikes to a hitter. (A foul ball counts as a strike, but it cannot be the third and final strike of the at-bat. A foul tip, which is caught by the catcher, is considered a third strike.)

Stolen Base (SB)

A stolen base occurs when a baserunner advances by taking a base to which he isn't entitled. This generally occurs when a pitcher is throwing a pitch, but it can also occur while the pitcher still has the ball or is attempting a pickoff, or as the catcher is throwing the ball back to the pitcher.

Stolen-base Percentage (SB%)

Stolen-base percentage is determined by the number of steals for a player divided by his total number of attempts. SB% is an essential tool in evaluating base stealers, because the league leaders in stolen bases often get thrown out frequently, too. In that vein, stolen bases are useful -- but only if a base stealer isn't at a high risk of getting thrown out.


Steamer is a system of projections developed by Jared Cross -- a high school science teacher in Brooklyn -- and two of his former students, Dash Davidson and Peter Rosenbloom. It is currently used by Fangraphs as its primary projection system for individual players.

Starting Pitcher

Starting pitchers stand on the pitching mound, which is located in the center of the infield and 60 feet, six inches away from home plate.

Sprint Speed (SS)

Introduced during the 2017 season, Sprint Speed is a Statcast metric that aims to more precisely quantify speed by measuring how many feet per second a player runs in his fastest one-second window.

Splitter (FS)

A pitcher throws a splitter by gripping the ball with his two fingers "split" on opposite sides of the ball. When thrown with the effort of a fastball, the splitter will drop sharply as it nears home plate.

Split Contract

A split contract calls for a player to earn different salaries in the Majors Leagues and Minor Leagues. On player on a split contract would earn the pro-rated portion of his Major League salary for any time spent on the Major League roster. That is determined by dividing his Major League salary by 183 (the number of days in the MLB regular season) and multiplying that number by the number of days spent on the Major League roster.

Spin Rate (SR)

A pitcher's Spin Rate represents the rate of spin on a baseball after it is released. It is measured in revolutions per minute.

Spectator Interference

In every case of spectator interference with a batted or thrown ball, the ball shall be declared dead and the baserunners can be placed where the umpire determines they would have been without the interference. When a spectator clearly prevents a fielder from catching a fly ball by reaching onto the field of play, the batter shall be ruled out. But no interference is called if a spectator comes in contact with a batted or thrown ball without reaching onto the field of play -- even if a fielder might have caught the ball had the spectator not been there.


A "southpaw" is a left-handed pitcher.

Slugging Percentage (SLG)

Slugging percentage represents the total number of bases a player records per at-bat. Unlike on-base percentage, slugging percentage deals only with hits and does not include walks and hit-by-pitches in its equation.

Slide Rule

When sliding into a base in an attempt to break up a double play, a runner has to make a "bona fide slide." Such is defined as the runner making contact with the ground before reaching the base, being able to reach the base with a hand or foot, being able to remain on the base at the completion of the slide (except at home plate) and not changing his path for the purpose of initiating contact with a fielder. The slide rule prohibits runners from using a "roll block" or attempting to initiate contact with the fielder by elevating and kicking his leg above the fielder's knee, throwing his arm or his upper body or grabbing the fielder. When a violation of the slide rule occurs, the offending runner and the batter-runner will be called out.

Slider (SL)

A slider is a breaking pitch that is thrown faster and generally with less overall movement than a curveball. It breaks sharply and at a greater velocity than most other breaking pitches. The slider and the curveball are sometimes confused because they generally have the same purpose -- to deceive the hitter with spin and movement away from a pitcher's arm-side. (When a pitch seems to toe the line between the two, it is referred to in slang as a "slurve.")

Slash Line

Slash line is a colloquial term used to represent a player's batting average, on-base percentage and slugging percentage. Those three stats are often referenced together in baseball media with forward slashes separating them, which is where the term slash line comes from.

Skill-interactive Earned Run Average (SIERA)

SIERA quantifies a pitcher's performance by trying to eliminate factors the pitcher can't control by himself. But unlike a stat such as xFIP, SIERA considers balls in play and adjusts for the type of ball in play.

Sinker (SI)

The sinker is a pitch with hard downward movement, known for inducing ground balls. It's generally one of the faster pitches thrown and, when effective, induces some of the weakest contact off the bats of opposing hitters.

Single (1B)

A single occurs when a batter hits the ball and reaches first base without the help of an intervening error or attempt to put out another baserunner. Singles are the most common type of hit in baseball, and they occur in many varieties. If a batter beats out a bunt or an infield dribbler -- it's a single. And if a batter hits a rocket to the outfield wall but is held at first base -- it's also a single. (A batter is still credited with a single if he reaches first safely but is thrown out while trying to advance to second.)

Shutout (SHO)

A starting pitcher is credited with a shutout when he pitches the entire game for a team and does not allow the opposition to score. By definition, any pitcher who throws a shutout is also awarded a win. Because he recorded every out for his team and didn't allow a run, his team could only have won.


The shortstop positions himself between the third baseman and the second-base bag.


A shift is a term used to describe the situational defensive realignment of fielders away from their "traditional" starting points. Infield shifts and outfield shifts are tracked separately. In 2017, lefty batters were shifted against on 22.1 percent of their plate appearances, while righty batters saw a shift on 5.2 percent of their plate appearances.

Set Position

Pitchers are permitted to use two legal pitching deliveries -- the windup position and the set position -- and either position may be used at any time.

Service Time

Players receive Major League service time for each day spent on the 26-man roster (it was 25, prior to 2020) or the Major League injured list. Important to players and clubs alike, service time is used to determine when players are eligible for arbitration as well as free agency.

Seeing-eye Single

A "seeing-eye single" is a softly or moderately struck ground ball that goes between infielders for a base hit.

Second Baseman

The second baseman positions himself between the first- and second-base bags (closer to second base), typically toward the back of the infield dirt.

Screwball (SC)

A screwball is a breaking ball designed to move in the opposite direction of just about every other breaking pitch. It is one of the rarest pitches thrown in baseball, mostly because of the tax it can put on a pitcher's arm. The movement on the screwball -- which travels toward the pitcher's arm side -- is caused by an extremely unorthodox throwing motion.

Scouting Grades

Scouting grades have been a staple of's prospect coverage for years, and they generally match how clubs grade players as well.

Save (SV)

A save is awarded to the relief pitcher who finishes a game for the winning team, under certain circumstances. A pitcher cannot receive a save and a win in the same game.

Save Percentage (SV%)

Save percentage represents the percent of time a pitcher records a save when given a save opportunity. Obviously, then, save percentage is calculated by dividing a pitcher's total number of saves by his total number of save opportunities.

Save Opportunity (SVO)

A save opportunity occurs every time a relief pitcher either records a save or a blown save. For a save opportunity, a pitcher must be the final pitcher for his team (and not the winning pitcher) and do one of the following:

Salary Arbitration

Players who have three or more years of Major League service but less than six years of Major League service become eligible for salary arbitration if they do not already have a contract for the next season. Players who have less than three but more than two years of service time can also become arbitration eligible if they meet certain criteria; these are known as "Super Two" players. Players and clubs negotiate over salaries, primarily based on comparable players who have signed contracts in recent seasons. A player's salary can indeed be reduced in arbitration -- with 20 percent being the maximum amount by which a salary can be cut.

Sacrifice Fly (SF)

A sacrifice fly occurs when a batter hits a fly-ball out to the outfield or foul territory that allows a runner to score. The batter is given credit for an RBI. (If the ball is dropped for an error but it is determined that the runner would have scored with a catch, then the batter is still credited with a sacrifice fly.)

Sacrifice Bunt (SH)

A sacrifice bunt occurs when a player is successful in his attempt to advance a runner (or multiple runners) at least one base with a bunt. In this vein, the batter is sacrificing himself (giving up an out) in order to move another runner closer to scoring. When a batter bunts with a runner on third base, it is called a squeeze play and, if successful, is still recorded as a sacrifice.

Run Support Per Nine Innings (RS/9)

Run support per nine innings measures how many runs an offense scores for a certain pitcher while that pitcher is in the game. That number is then set over a nine-inning timeframe. So the stat essentially answers the question, "How many runs of support does a pitcher receive per nine innings?"

Runs Created (RC)

Runs Created estimates a player's offensive contribution in terms of total runs. It combines a player's ability to get on base with his ability to hit for extra bases. Then it divides those two by the player's total opportunities.

Runs Batted In (RBI)

A batter is credited with an RBI in most cases where the result of his plate appearance is a run being scored. There are a few exceptions, however. A player does not receive an RBI when the run scores as a result of an error or ground into double play.

Runs Allowed Per Nine Innings Pitched (RA9)

Runs allowed per nine innings pitched -- the title says it all. It's basically ERA with the "E" removed.

Run (R)

A player is awarded a run if he crosses the plate to score his team a run. When tallying runs scored, the way in which a player reached base is not considered. If a player reaches base by an error or a fielder's choice, as long as he comes around to score, he is still credited with a run. If a player enters the game as a pinch-runner and scores, he is also credited with a run.

Run Differential

A team's run differential is determined by subtracting the total number of runs (both earned and unearned) it has allowed from the number of runs it has scored.

Rule 5 Draft

Held each December, the Rule 5 Draft allows clubs without a full 40-man roster to select certain non-40-man roster players from other clubs. Clubs draft in reverse order of the standings from the previous season. Players signed at age 18 or younger need to be added to their club's 40-Man roster within five seasons or they become eligible for the Rule 5 Draft. Players who signed at age 19 or older need to be protected within four seasons.

Rule 4 Draft

The Rule 4 Draft is the official term for the First-Year Player Draft, an amateur draft held annually in early June. Players must be a resident of the United States (U.S. territories, such as Puerto Rico, apply) or Canada to be eligible for the draft. Players who have graduated high school but not attended college are eligible for the draft, as are those who have completed at least one year of junior college. Players attending four-year colleges are eligible to be drafted upon completing their junior year or turning 21 years old.

Rookie Eligibility

A player shall be considered a rookie unless he has exceeded any of the following thresholds in a previous season (or seasons):

Right Fielder

The right fielder covers the right portion of the outfield grass (when viewing the field from home plate).

Retention Bonus (Article XX(B) Free Agents)

If a club signs an Article XX(B) free agent to a Minor League contract between a period after the conclusion of the World Series and 10 days before the start of the next season, it must decide by noon ET five days before Opening Day whether it will add the player to its 26-man roster or MLB injured list at the outset of the season.

Replay Review

Replay review in Major League Baseball is designed to provide timely review of certain disputed calls and is initiated by a manager challenge or by the umpire crew chief.

Relief Win (RW)

A relief win is defined as any win by a pitcher who was not the starting pitcher. Relievers can earn relief wins in two different ways -- one far more common than the other. First, if a reliever is in the game at the time his team takes the lead for good, he is credited with the victory. A reliever can also pick up the win if the starting pitcher pitches fewer than five innings in what would have been the starter's win, and the official scorer deems that reliever to have been the "most effective" in preserving the win.

Relief Pitcher

Relief pitchers stand on the pitching mound, which is located in the center of the infield and 60 feet, six inches away from home plate.

Release Waivers

Before a club can formally release a player, that player must first be passed through unconditional release waivers. All 29 other clubs in the Majors have the opportunity to claim the player and add him to their 40-man rosters. A player that is claimed on release waivers has the option of rejecting that claim and instead exploring the free-agent market. Release waivers are often requested after a player's contract is designated for assignment or in cases when a veteran player would otherwise refuse an outright assignment. Players are rarely claimed off release waivers, as the claiming club is required to pick up the remaining contract. Once the player clears waivers, the releasing club is responsible for the old contract.

Regulation Game

A game is considered a regulation game -- also known as an "official game" -- once the visiting team has made 15 outs (five innings) and the home team is leading, or once the home team has made 15 outs regardless of score.

Reached On Error (ROE)

A batter receives a reached on error when he reaches base because of a defensive error -- meaning he wouldn't have otherwise reached.

Range Factor (RF)

Range Factor is determined by dividing the sum of a fielder's putouts and assists by his total number of defensive games played.

Quality Start (QS)

A starting pitcher records a quality start when he pitches at least six innings and allows three earned runs or fewer. A starting pitcher has two jobs: to prevent runs and get outs. The quality start statistic helps to quantify which pitchers did a "quality" job in those two departments.

Qualifying Offer

The qualifying offer is a competitive balance measure that was implemented as part of the 2012-16 Collective Bargaining Agreement and restructured under the 2017-21 Collective Bargaining Agreement.

Putout (PO)

A fielder is credited with a putout when he is the fielder who physically records the act of completing an out -- whether it be by stepping on the base for a forceout, tagging a runner, catching a batted ball, or catching a third strike. A fielder can also receive a putout when he is the fielder deemed by the official scorer to be the closest to a runner called out for interference.

Putaway Percentage

Putaway Percentage (PutAway%) is the rate of two-strike pitches that result in a strikeout.

Protested Game

Managers can protest a game when they allege that the umpires have misapplied the rules. The umpires must be notified of the protest at the time the play in question occurs and before the next pitch or attempted play begins. If the play in question ended the game, a protest can be filed with the league office until noon the following day. No protests are permitted on judgment calls by the umpires.

Projected Home Run Distance (HR-DIS)

Projected Home Run Distance represents the distance a home run ball would travel if unhindered by obstructions such as stadium seats or walls. This metric is determined by finding the parabolic arc of the baseball and projecting the remainder of its flight path.

Postseason Share

Each postseason team receives a share of the money earned from playoff gate receipts. The World Series champion receives the highest percentage of the pool, followed by the World Series runner-up, and so on.

Postseason Roster Rules & Eligibility

In a typical season, any player who is on the 40-man roster or 60-day injured list as of 11:59 p.m. ET on Aug. 31 is eligible for the postseason.

Pop-up Rate (PO%)

Pop-up rate represents the percentage of balls hit into the field of play that are characterized as pop-ups. Each ball that is hit into the field of play is characterized as a line drive, a fly ball, a ground ball or a pop-up. (A fly ball is a fly to the outfield, while a pop-up is hit to the infield.) Pop-up rate can be used as a metric to evaluate both hitters and pitchers.

Pop Time (POP)

On steal or pickoff attempts by a catcher, Pop Time represents the time elapsed from the moment the pitch hits the catcher's mitt to the moment the intended fielder is projected to receive his throw at the center of the base.

Player to Be Named Later (PTBNL)

When clubs consent to include a player to be named later (often abbreviated PTBNL) in a trade, they agree to decide upon or announce the final player involved in that trade at a later date.

Player Option

A player option is an optional year at the end of a contract that can be applied at the player's discretion. In such cases, the player has the right to exercise his option and lock in that optional salary as a guaranteed sum or reject the option in favor of testing free agency.

Player Empirical Comparison and Optimization Test Algorithm (PECOTA)

Also a "backronym" for former Major Leaguer Bill Pecota, PECOTA is Baseball Prospectus' system for projecting player performance. The acronym stands for "Player Empirical Comparison and Optimization Test Algorithm." It was developed by Nate Silver in 2003, and Silver ran the projections - which were owned by Baseball Prospectus -- from '03-09, before ceding full responsibility to Baseball Prospectus itself.

Plate Appearances Per Strikeout (PA/SO)

Plate appearances per strikeout is a basic ratio determined by dividing a player's total plate appearances by his number of strikeouts. Hitters who don't strike out very much will have high PA/SO marks.

Plate Appearance (PA)

A plate appearance refers to a batter's turn at the plate. Each completed turn batting is one plate appearance. Plate appearances can often be confused with at-bats. But unlike with at-bats -- which only occur on certain results -- a plate appearance takes into account every single time a batter comes up and a result between batter and pitcher is obtained.

Plantar Fasciitis

The plantar fascia is a thick, web-like band of ligament that runs along the sole of the foot, from the bottom of the heel to the base of the toes. It keeps the arch of the foot from flattening completely when the foot is bearing weight, thus providing cushioning and shock absorption. The plantar fascia also allows you to point your toes.

Pitch Movement

The movement of a pitch is defined in inches, both in raw numbers and (more importantly) as a measurement against average. It is displayed separately for horizontal break and vertical drop.

Pitching Coach

Pitching coaches instruct their pitchers on pitching mechanics, pitch selection and preparation while also providing insight into the weaknesses of opposing hitters -- often with the help of video technology.

Pitches Per Start (P/GS)

Pitches per start tells us how many pitches a starting pitcher throws, on average, in his starts. It can be a useful tool for evaluating pitchers in many ways -- particularly while he's pitching. P/GS gives the viewer an indication of just how much a starting pitcher might have left in the tank.

Pitches Per Plate Appearance (P/PA)

P/PA is a simple stat that quantifies how many pitches are thrown per plate appearance. It can be used for both hitters and pitchers, although it is more frequently referred to when assessing hitters.

Pitches Per Inning Pitched (P/IP)

Pitches per inning pitched is a tool used to evaluate how efficient a pitcher is at getting his outs -- or how many pitches he typically needs to use to do his job. Calculating the number is easy enough. It's found by dividing a pitcher's total number of pitches thrown by his total number of innings pitched.

Pickoff (PK)

A pickoff occurs between pitches when a pitcher throws a ball to a fielder, who eventually puts out or assists in retiring an opposing baserunner. An illegal pickoff attempt results in a balk.


A "pickle" is a rundown.

Perceived Velocity (PV)

Perceived Velocity is an attempt to quantify how fast a pitch appears to a hitter, by factoring the Velocity of the pitch and the release point of the pitcher. It takes Velocity one step further -- because a 95 mph fastball will reach a hitter faster if the pitcher releases the ball seven feet in front of the rubber instead of six.

Passed Ball (PB)

A catcher is given a passed ball if he cannot hold onto a pitch that -- in the official scorer's judgment -- he should have, and as a result at least one runner moves up on the bases. Passed balls have commonality with wild pitches, as both allow a runner to advance on his own without a stolen base. However, there is a key difference: A passed ball is deemed to be the catcher's fault, while a wild pitch is deemed to be the fault of the pitcher.

Partner Leagues

The American Association, Frontier League, Atlantic League and Pioneer League are independent baseball leagues that have been designated as Partner Leagues of MLB.

Painting the Black

A pitcher is said to be "painting the black" when he throws a pitch that barely catches the outside or inside corner of the plate for a strike.

Pace of Play

A number of changes have been implemented to improve the pace of play since the 2014 season.

Outs Above Average (OAA)

Outs Above Average (OAA) is a range-based metric of skill that shows how many outs a player has saved. Prior to 2020, OAA was an outfield-only metric. But it has been expanded to include infielders. OAA is calculated differently for outfielders and infielders (details below).

Outright Waivers

A club attempting to remove a player from the 40-man roster and send him to the Minor Leagues must first place that player on outright waivers, allowing the 29 other Major League clubs the opportunity to claim him. The claiming club assumes responsibility for the remaining money owed to the claimed player, who is placed on his new club's 40-man roster. Should the player clear waivers, he can be sent to any Minor League affiliate the club chooses. Outright waivers are also used when clubs wish to remove a player who is out of Minor League options from the 26-man roster (it was 25, prior to 2020) by sending him to the Minors.

Out (O)

One of baseball's most basic principles, an out is recorded when a player at bat or a baserunner is retired by the team in the field. Outs are generally recorded via a strikeout, a groundout, a popout or a flyout, but MLB's official rulebook chronicles other ways -- including interfering with a fielder -- by which an offensive player can be put out.

Outfield Assist (OFA)

An outfielder records an assist when he throws the ball into the infield and an out is recorded as a result. Outfield assists are one of the most commonly referenced types of assists.

Ordinary Effort

Ordinary effort refers to the effort that a fielder of average skill at a specific position should exhibit on a play, with due consideration given to the conditions of the playing field and the weather. Umpires must use that standard when calling infield fly plays, and the official scorer uses it to judge what constitutes an error, a wild pitch, a passed ball and a sacrifice.


An "opener" is a pitcher -- normally a reliever -- who starts a game for purposes of matching up against the top of the opponent's lineup in the first inning, which has traditionally been the highest-scoring inning, before being relieved by a pitcher who would otherwise function as a starter. This allows for a team to counter its opponent's first three batters with the pitcher it feels has the best chance for success against them.

On-base Plus Slugging Plus (OPS+)

OPS+ takes a player's on-base plus slugging percentage and normalizes the number across the entire league. It accounts for external factors like ballparks. It then adjusts so a score of 100 is league average, and 150 is 50 percent better than the league average.

On-base Plus Slugging (OPS)

OPS adds on-base percentage and slugging percentage to get one number that unites the two. It's meant to combine how well a hitter can reach base, with how well he can hit for average and for power.


Oliver is a system of player projections developed by Brian Cartwright and used by The Hardball Times. For projecting returning Major League players, it uses a somewhat basic formula: Three years of player data with the most recent years weighted heavier, while also factoring age and regression to the mean.

Official Scorer

The official scorer is the person appointed to observe from the press box and record the outcome of everything that happens during a game, and to make judgment calls that affect the official record of said game. The official scorer files a report after each game for documentation purposes.


Obstruction describes an act by a fielder, who is not in possession of the ball or in the process of fielding it, that impedes the baserunner's progress.

Oblique Strain

The oblique muscles lie alongside the rectus abdominis muscles -- the ones that make up the "six pack" -- and are responsible for core control and rotation. The internal oblique sits under the external oblique and is the most commonly injured abdominal or core muscle in baseball because it is the most activated core muscle during hitting and throwing.

Number of Pitches (NP)

A pitcher's total number of pitches is determined by all the pitches he throws in live game action, including strikes, unintentional balls and intentional balls.

No-trade Clause

A no-trade clause is a contractual clause that allows players to veto trades to certain teams. No-trade clauses are often worked into contract extensions and free-agent contracts as a perk for the players signing such deals.


When a club "non-tenders" a player, it declines to give that player a contract for the upcoming season, thereby immediately making him a free agent. Players on the 40-man roster with fewer than six years of Major League service time must be tendered contracts each offseason by a set deadline -- typically a date in early December -- or non-tendered and released to the free-agent pool.

Non-roster Invite (NRI)

A non-roster invite (NRI) is an invitation for a player who is not on a club's 40-man roster to attend Major League camp in Spring Training and compete for a roster spot. Clubs can extend NRIs to their upper-level Minor Leaguers and also include NRIs in Minor League contracts given to free agents in the offseason.

Non-guaranteed Contract

Players who are on arbitration (unless specified at the time of the agreement), Minor League or split contracts are not fully guaranteed their salaries.

Neighborhood Play

The "neighborhood play" is a colloquial term used to describe the leeway granted to middle infielders with regards to touching second base while in the process of turning a ground-ball double play. Though it is not explicitly mentioned in the rulebook, middle infielders were long able to record an out on the double-play pivot simply by being in the proximity -- or neighborhood -- of the second-base bag. The maneuver had been permitted for safety purposes, as it allowed the pivot man to get out of the way of the oncoming baserunner as quickly as possible.

Mutual Option

A mutual option is an optional year at the end of a contract. In order for the optional year to become guaranteed, both parties must agree to exercise the option.

Mound Visit

The members of the coaching staff (including the manager) can make one mound visit per pitcher per inning without needing to remove the pitcher from the game. If the same pitcher is visited twice in one inning, the pitcher must be removed from the contest. These mound visits are limited to 30 seconds, starting when the manager or coach has exited the dugout and been granted time by the umpire. The mound visit is considered to be concluded once the manager or coach leaves the 18-foot circle surrounding the pitching rubber, though they are permitted to temporarily leave that area to notify the umpire of a substitution. In that case, the manager or coach can then return to the mound without it being counted as two mound visits.

MLB Draft League

Announced in November 2020, the MLB Draft League will give eligible prospects a chance to showcase their abilities and gain exposure prior to the MLB Draft.

Minor League Options

Players on a 40-man roster are given three Minor League "options." An option allows that player to be sent to the Minor Leagues ("optioned") without first being subjected to waivers. Players who are optioned to the Minors are removed from a team's active 26-man roster but remain on the 40-man roster.

Mendoza Line

The "Mendoza Line" is a .200 batting average.

Manager Challenge

Each club receives two manager challenges to start each All-Star Game, postseason game and Divisional or Wild Card tiebreaker game, and one manager challenge to start every other game. All reviews are conducted at the Replay Command Center, which is located at Major League Baseball Advanced Media headquarters in New York, by replay officials -- full-time Major League umpires who work shifts at the Replay Command Center in addition to their on-field work. Replay officials review all calls subject to replay review and decide whether to change the call on the field, confirm the call on the field or let stand the call on the field due to the lack of clear and convincing evidence.


Field managers are responsible for writing out the daily lineup and making in-game tactical decisions (e.g. pitching changes and decisions regarding pinch-hitting, pinch-running and defensive replacements). Often viewed as a face of his franchise, managers also play a crucial role in interacting with the media before and after games and managing the atmosphere in the clubhouse.

Major League Baseball Logo

The official logo of Major League Baseball was designed by Jerry Dior in 1968, when MLB commissioned the marketing firm Dior worked at to create a logo for the centennial celebration of professional baseball, set to take place in 1969. The logo first appeared on uniforms during the 1969 season.

Magic Number (MN)

In baseball, the phrase "magic number" is used to determine how close a team is to making the playoffs or winning the division. It becomes prominent every year in September as teams begin closing in on clinching.


A Maddux describes a start in which a pitcher tosses a complete-game shutout on fewer than 100 pitches. Named after Hall of Famer Greg Maddux, the term was coined by baseball writer Jason Lukehart.

Loss (L)

A pitcher receives a loss when a run that is charged to him proves to be the go-ahead run in the game, giving the opposing team a lead it never gives up. Losses are almost always paired with wins when used to evaluate a pitcher, creating a separate pitching term known as win-loss record.

Lisfranc Injury

The Lisfranc joint complex, named for the French surgeon who first described it in the 1800s, includes the five metatarsal bones along with the tendons and ligaments that connect the mid-foot to the forefoot and form the arch at the top of the foot. Ligaments and tendons in this area can be sprained, and the bones can be fractured. Lisfranc injuries can be the result of a trauma, such as a collision, or they can be caused indirectly by a sudden rotational force in the mid-foot.

Line-drive Rate (LD%)

Line-drive rate represents the percentage of balls hit into the field of play that are characterized as line drives. Each ball that is hit into the field of play is characterized as a line drive, a fly ball, a ground ball or a pop-up. Line-drive rate can be used as a metric to evaluate both hitters and pitchers.

Leverage Index (LI)

Created by Tom Tango, Leverage Index measures the importance of a particular event by quantifying the extent to which win probability could change on said event, with 1.0 representing a neutral situation.

Left On Base (LOB)

Left on base can be viewed as both an individual statistic or as a team statistic.

Left Fielder

The left fielder covers the left portion of the outfield grass (when viewing the field from home plate).

Lead Distance (LEAD)

Lead Distance represents the distance between the base and the baserunner's center of mass as the pitcher makes his first movement -- either to home or to the base on a pickoff attempt.

Launch Angle (LA)

Launch Angle represents the vertical angle at which the ball leaves a player's bat after being struck. Average Launch Angle (aLA) is calculated by dividing the sum of all Launch Angles by all Batted Ball Events.

Lat Strain

The latissimus dorsi is the broadest muscle of the back. It extends from the top of the hip to the lower six thoracic vertebrae in the mid-back and up to the top of the humerus -- the bone in the upper arm that forms the ball of the ball-and-socket shoulder joint -- at the front of the shoulder.

Late-inning Pressure Situation (LIPS)

Late-inning pressure situations are defined as any at-bat in the seventh inning or later where the batter's team trails by three runs or fewer, is tied or is ahead by only one run. If the bases are loaded and the batting team trails by four runs, this also counts as a late-inning pressure situation.

Korean Posting System

Players from Korea's top league -- the Korea Baseball Organization (KBO) -- who do not have the requisite nine years of professional experience to gain international free agency can request to be "posted" for Major League clubs. When a KBO club posts a player, all 30 Major League clubs are allowed to negotiate with the player and his representative for a specific period of time. During the 2020-2021 offseason, that window begins on Nov. 10 and ends Dec. 14, according to Jee-ho Yoo of Yonhap News. To sign a posted player, an MLB team must pay a release fee to the KBO club, calculated based on the amount of his guaranteed contract. For Major League contracts, the KBO team receives a payment equal to 20% of the first $25 million in guaranteed value, 17.5% of the next $25 million, and 15% on all amounts above $50 million. When the posted player signs a Minor League contract, the KBO team receives a payment equal to 25% of the signing bonus. Under KBO rules, a club is allowed to post only one player at a time and cannot allow more than one player to leave via the posting process per offseason.

Knuckle-curve (KC)

The knuckle-curve is one of baseball's greatest paradoxes, given that a curveball is defined by its spin and a knuckleball is defined by its lack thereof. Still, the knuckle-curve produces the desired effect of the two pitches -- a slow, curveball break mixed with the unpredictable fluttering of the knuckleball.


A "K" is a strikeout.


Jump is a Statcast metric that shows which players have the fastest reactions and most direct routes in the outfield. It's defined as: "How many feet did he cover in the right direction in the first three seconds after pitch release?"


JAWS (Jaffe Wins Above Replacement Score) is a system created by Jay Jaffe that evaluates a player's worthiness for enshrinement in the National Baseball Hall of Fame by comparing him to the Hall of Famers at his position. The stated goal of JAWS is to maintain or improve the Hall of Fame's standards by electing players who are at least as good as the average Hall of Famer at those players' positions.

Japanese Posting System

Players from Japan's top league -- Nippon Professional Baseball (NPB) -- who do not have the requisite nine years of professional experience to gain international free agency can request to be "posted" for Major League clubs.

Isolated Power (ISO)

ISO measures the raw power of a hitter by taking only extra-base hits -- and the type of extra-base hit -- into account.

International Free Agency -- Cuba (Professional)

While most international free agents from Latin America sign as amateurs during their teenage years, Cuba has its own top professional league: the Cuban National Series (Serie Nacional). Players with enough experience as a professional in Cuba are exempt from MLB's international bonus pools.

International Free Agency -- Asia (Professional)

Players that accrue nine years of service time in Japan's Nippon Professional Baseball or the Korea Baseball Organization are considered free agents. Such players are eligible to pursue opportunities in any league, including Major League Baseball, without being subjected to the Korean or Japanese posting systems.

International Amateur Free Agency & Bonus Pool Money

As per the 2017-21 Collective Bargaining Agreement, clubs are each subject to a spending cap for amateur international free agents. Each club will have at least a $4.75 million bonus pool to spend, with those that have a pick in Competitive Balance Round A receiving $5.25 million and those with a pick in Competitive Balance Round B receiving $5.75 million.

Intercostal Strain

The 11 intercostal muscles on each side of the rib cage connect one rib to another, working to spread the ribs apart and bring them back together again as the chest expands and contracts during breathing. The intercostals are also part of the core muscle group that is integral to many fundamental baseball movements. They are most often injured during a sudden contraction when they are in a stretched position, such as during a throw or swing. Because the lungs are located inside the rib cage, pain from a strained intercostal can be so severe that it feels like a broken rib.

Intentional Walk (IBB)

An intentional walk occurs when the defending team elects to walk a batter on purpose, putting him on first base instead of letting him try to hit. Intentional walks -- which count as a walk for the hitter and a walk allowed by the pitcher -- are an important strategy in the context of a game. They can be used to put a runner on first base, setting up a potential double play.

Innings Played (INN)

Innings played is a defensive statistic determined by counting the number of outs during which a player is in the field and dividing by three.

Innings Pitched (IP)

Innings pitched measures the number of innings a pitcher remains in a game. Because there are three outs in an inning, each out recorded represents one-third of an inning pitched.

Innings Per Start (I/GS)

Innings per start signifies the average number of innings a pitcher throws per game started and is determined by dividing his innings pitched by his starts.

Inherited Runs Allowed Percentage (IR-A%)

IR-A% denotes the percentage of inherited runners who come around to score against a relief pitcher. It is determined by dividing the inherited runs scored against a pitcher by the total number of runners he has inherited. This statistic essentially asks the question: How often does a relief pitcher allow a runner (or multiple runners) to score when he enters the game with a runner (or multiple runners) on base?

Infield Fly

An infield fly is any fair fly ball (not including a line drive or a bunt) which can be caught by an infielder with ordinary effort when first and second or first, second and third base are occupied, before two men are out. The rule is in place to protect against a team allowing a shallow fly ball to drop in with the intention of causing a force play at second and third or second, third and home. Otherwise, the team would be able to force out baserunners who had stayed put on a routine fly ball.

Incentive Clause

Incentives in contracts allow players to earn additional money by achieving certain predetermined benchmarks. Major League Baseball's Basic Agreement prohibits incentives from being awarded based on statistical achievement. Thus, playing time is the near-universal means by which players receive incentives. Pitchers with incentive-laden contracts typically trigger the incentives based on number of innings pitched, number of games started, number of relief appearances, number of games finished, etc. Hitters will most commonly trigger incentives based on plate appearances. Some contracts also contain roster bonuses, which reward a player simply for staying on the active roster for a certain number of days.

Home To First

Home to First readings measure the time elapsed from the point of bat-on-ball contact to the moment the batter reaches first base. Statcast has the ability to filter Home to First readings, which can be useful when attempting to discern a hitter's ability to "beat out" a ground ball hit to an infielder. In some scouting circles, a hitter's Home to First time on infield ground balls is sometimes referred to as "dig speed."

Home Run To Fly Ball Rate (HR/FB)

Home-run-to-fly-ball (HR/FB) rate is the rate at which home runs are hit against a pitcher for every fly ball he allows. It's as simple as the name makes it sound. The league average HR/FB rate is usually slightly below 10 percent.

Home Runs Per Nine Innings (HR/9)

HR/9 represents the average number of home runs allowed by a pitcher on a nine-inning scale. The statistic is determined by dividing a pitcher's home runs allowed by his total innings pitched and multiplying the result by nine.

Home Run (HR)

A home run occurs when a batter hits a fair ball and scores on the play without being put out or without the benefit of an error.

Hold (HLD)

A hold occurs when a relief pitcher enters the game in a save situation and maintains his team's lead for the next relief pitcher, while recording at least one out. One of two conditions must be met for a pitcher to record a hold: 1) He enters with a lead of three runs or less and maintains that lead while recording at least one out. 2) He enters the game with the tying run on-deck, at the plate or on the bases, and records an out.

Hitting Coach

Hitting coaches instruct players on matters related to hitting, such as batting mechanics, plate discipline and preparation.

Hits Per Nine Innings (H/9)

H/9 represents the average number of hits a pitcher allows per nine innings pitched. It is determined by dividing a pitcher's hits allowed by his innings pitched and multiplying that by nine. It's a very useful tool for evaluating pitchers, whose goal is to prevent runs, which are usually scored by hits.

Hit (H)

A hit occurs when a batter strikes the baseball into fair territory and reaches base without doing so via an error or a fielder's choice. There are four types of hits in baseball: singles, doubles, triples and home runs. All four are counted equally when deciphering batting average. If a player is thrown out attempting to take an extra base (e.g., turning a single into a double), that still counts as a hit.

Hit Distance (DST)

Hit Distance represents the distance away from home plate that a batted ball lands -- whether by hitting the ground, the seats, the wall or a fielder's glove.

Hit-by-pitch (HBP)

A hit-by-pitch occurs when a batter is struck by a pitched ball without swinging at it. He is awarded first base as a result. Strikes supersede hit-by-pitches, meaning if the umpire rules that the pitch was in the strike zone or that the batter swung, the HBP is nullified.

Hard-hit Rate

Statcast defines a 'hard-hit ball' as one hit with an exit velocity of 95 mph or higher, and a player's "hard-hit rate" is simply showing the percentage of batted balls that were hit at 95 mph or more.

Hamstring Strain

At the back of each thigh are three hamstring muscles -- the semitendinosus, semimembranosus and biceps femoris, from the inside to the outside. At the top, or proximal end, the three muscles come together, form the hamstring tendon and attach at the base of the pelvis on the ischial tuberosity, or the sitting bone. They run down the back of the thigh, cross the knee joint and attach distally to the tibia and fibula bones in the lower leg. The hamstring muscle group is responsible for the flexing of the lower leg at the knee.

Guaranteed Contract

Players who obtain Major League contracts -- either via free agency or extensions -- are guaranteed the full amount of money promised by those contracts. Conversely, players signed to Minor League contracts must earn a spot on the roster in Spring Training or via an in-season promotion in order to have their contracts guaranteed. Arbitration contracts are not guaranteed either, as a club can release a player on or before the 16th day of Spring Training and be responsible for only 30 days worth of pay. Players cut between the 17th and the final day of Spring Training must be compensated for 45 days worth of pay (at the prorated version of their arbitration salary). But if a player that agreed to an arbitration salary breaks camp with the club, his contract is fully guaranteed.

Ground Rules

The Commissioner's Office issues a list of universal ground rules that are to be used in every Major League ballpark each season. Individual parks then are able to institute their own special ground rules, covering instances in which the intricacies of said parks might influence the game. For example, Tropicana Field has a number of special ground rules regarding occurrences of a batted ball striking a catwalk, light or another suspended object.

Groundout-to-Airout Ratio (GO/AO)

Groundout-to-airout ratio is obtained by dividing the total number of ground balls converted into outs (not including bunts) by the total number of balls in the air (fly balls and line drives) converted into outs.


A groundout occurs when a batter hits a ball on the ground to a fielder, who records an out by throwing to or stepping on first base. It can also occur when the batter reaches first base -- and the defense instead opts to record an out elsewhere via a "fielder's choice."

Ground Into Double Play (GIDP)

A GIDP occurs when a player hits a ground ball that results in multiple outs on the bases. The most common double plays are ground balls where a forceout is made on the player running from first to second base, then another forceout is made on the batter running to first base.

Ground-ball Rate (GB%)

Ground-ball rate represents the percentage of balls hit into the field of play that are characterized as ground balls. Each ball that is hit into the field of play is characterized as a line drive, a fly ball, a ground ball or a pop-up. Ground-ball rate can be used as a metric to evaluate both hitters and pitchers.

Grand Slam (GSH)

A grand slam occurs when a batter hits a home run with men on first base, second base and third base. Four runs score on a grand slam -- the most possible on one play -- and a batter is awarded four RBIs.

General Manager

In most organizations, the general manager has final say in terms of roster decisions (e.g. trades, free-agent signings) and coaching/front office personnel (e.g. hiring, firing, promotions, reassignments). In organizations that employ a president of baseball operations, the general manager is considered second in command. Not every club employs a president of baseball operations, though some examples include the 2016 Cubs (Theo Epstein), '16 Dodgers (Andrew Friedman) and '16 Indians (Chris Antonetti).

Games Started (GS)

A pitcher is credited with a game started if he is the first pitcher to throw a pitch for his team in a given game. A starter who pitches a full season in a five-man rotation will generally tally at most 34 games started. There is no minimum innings plateau for a pitcher to earn a game started, but a starter must pitch at least five innings to be eligible for a win.

Games Played (G)

A player is credited with having played a game if he appears in it at any point -- be it as a starter or a replacement. It's important to note that the player doesn't necessarily need an at-bat. He can also enter for defense or as a pinch-runner.

Games Finished (GF)

A pitcher is credited with a game finished if he is the last pitcher to pitch for his team in a given game, provided he was not the starting pitcher. Starters are not credited for a game finished when they pitch a complete game.

Game Score

Game Score measures a pitcher's performance in any given game started. Introduced by Bill James in the 1980s and updated by fellow sabermetrician Tom Tango in 2014, Game Score is presented as a figure between 0-100 -- except for extreme outliers -- and usually falls between 40-70.

Free Agency

Players become free agents upon reaching six years of Major League service time or when they are released from their organization prior to reaching six years of service time. A free agent is eligible to sign with any club for any terms to which the two parties can agree. If a player with fewer than six years of service time signs with a club, he remains under the control of that club until reaching the requisite service time to reach free agency -- even if the contract he signed does not cover the remaining years until that point.

Four-Seam Fastball (FA)

A four-seam fastball is almost always the fastest and straightest pitch a pitcher throws. It is also generally the most frequently utilized.

Foul Tip

A foul tip is a batted ball that goes sharply and directly to the catcher's hand or glove and is legally caught. A foul tip is considered equivalent to a ball in which the batter swings and misses, in that the baserunners are able to advance at their own risk (without needing to tag up). Should the batter produce a foul tip after previously accruing two strikes, the foul tip is considered strike three and the batter is out.

Foul Ball

The foul lines and foul poles are used to demarcate fair territory and, thus, determine what constitutes a foul ball.

Forkball (FO)

One of the rarest pitches in baseball, the forkball is known for its severe downward break as it approaches the plate. Because of the torque involved with snapping off a forkball, it can be one of the more taxing pitches to throw.

Forearm Flexor Tendinitis

Repetitive motion can irritate, inflame or strain the flexor and pronator tendons in the forearm -- the ones that bend the wrist toward the palm -- where they attach to the medial epicondyle, which is the bony bump on the inside of the elbow that is actually the base of the humerus bone. Flexor tendinitis, also known as medial epicondylitis, can manifest as pain on the inside of the elbow, loss of range of motion or a popping or locking sensation.

Force Play

A force play occurs when a baserunner is no longer permitted to legally occupy a base and must attempt to advance to the next base. The defense can retire the runner by tagging the next base before he arrives, though not if the defensive team first forces out a trailing runner. In that instance, the force play is removed and the defense must tag the remaining runners to retire them.


A flyout occurs when a batter hits the ball in the air (not including balls designated as line drives) and an opposing defender catches it before it hits the ground or fence.

Fly-ball Rate (FB%)

Fly-ball rate represents the percentage of balls hit into the field of play that are characterized as fly balls. Each ball that is hit into the field of play is characterized as a line drive, a fly ball, a ground ball or a pop-up. (A fly ball is a fly to the outfield, while a pop-up is hit to the infield.)

First Baseman

The first baseman positions himself to the right of the first-base bag and toward the back of the infield dirt when no runner occupies first base or on the first-base bag after a batter reaches first base.

First-base Coach

The first-base coach stands in foul ground, just behind the first-base bag, and helps relay signals from the dugout to both batters and baserunners. First-base coaches often assist baserunners in picking the appropriate time to steal a base and alert baserunners as pitchers attempt to retire them via a pickoff throw. By rule, the first-base coach must stay within the designated coach's box on the first-base side of home plate prior to each pitch. The coach may leave said box to signal a player once a ball is in play, provided the coach does not interfere with the play.

Fielding Percentage (FPCT)

Fielding percentage answers the question: How often does a fielder or team make the play when tasked with fielding a batted ball, throwing a ball, or receiving a thrown ball for an out. The formula is simple: the total number of putouts and assists by a defender, divided by the total number of chances (putouts, assists and errors).

Fielding Independent Pitching (FIP)

FIP is similar to ERA, but it focuses solely on the events a pitcher has the most control over -- strikeouts, unintentional walks, hit-by-pitches and home runs. It entirely removes results on balls hit into the field of play.

Fielder Right of Way

Fielders have a right to occupy any space needed to catch or field a batted ball and also must not be hindered while attempting to field a thrown ball.

Field Dimensions

No Major League ballparks are exactly alike, but certain aspects of the field of play must be uniform across baseball.

Fair Ball

The foul lines and foul poles are used to demarcate fair territory and, thus, determine what constitutes a fair ball.

Extra-base Hit (XBH)

An extra-base hit is defined as any hit that is not a single, meaning doubles, triples and home runs are all considered extra-base hits. They are a good stat to look at to evaluate an offensive player's power -- and in some cases, his speed.

Extension (EXT)

A pitcher must begin his throwing motion while standing on the pitching rubber -- which is 60 feet, 6 inches away from home plate. This does not mean pitches are actually thrown from 60 feet, 6 inches away from the plate.

Expected Weighted On-base Average (xwOBA)

Expected Weighted On-base Average (xwOBA) is formulated using exit velocity, launch angle and, on certain types of batted balls, Sprint Speed.

Expected Slugging Percentage (xSLG)

Expected Slugging Percentage (xSLG) is formulated using exit velocity, launch angle and, on certain types of batted balls, Sprint Speed.

Expected Fielding Independent Pitching (xFIP)

xFIP finds a pitcher's FIP, but it uses projected home-run rate instead of actual home runs allowed. The home run rate is determined by that season's league average HR/FB rate.

Expected ERA (xERA)

Expected ERA, or xERA, is a simple 1:1 translation of Expected Weighted On-Base Average (xwOBA), converted to the ERA scale. xwOBA takes into account the amount of contact (strikeouts, walks, hit by pitch) and the quality of that contact (exit velocity and launch angle), in an attempt to credit the pitcher or hitter for the moment of contact, not for what might happen to that contact thanks to other factors like ballpark, weather, or defense.

Expected Batting Average (xBA)

Expected Batting Average (xBA) is a Statcast metric that measures the likelihood that a batted ball will become a hit.

Exit Velocity (EV)

Exit Velocity measures the speed of the baseball as it comes off the bat, immediately after a batter makes contact. This is tracked for all Batted Ball Events -- outs, hits and errors.

Error (E)

A fielder is given an error if, in the judgment of the official scorer, he fails to convert an out on a play that an average fielder should have made. Fielders can also be given errors if they make a poor play that allows one or more runners to advance on the bases. A batter does not necessarily need to reach base for a fielder to be given an error. If he drops a foul ball that extends an at-bat, that fielder can also be assessed an error.

Eephus (EP)

The eephus is one of the rarest pitches thrown in baseball, and it is known for its exceptionally low speed and ability to catch a hitter off guard.

Earned Run (ER)

An earned run is any run that scores against a pitcher without the benefit of an error or a passed ball. Often, it is the judgment of the official scorer as to whether a specific run would've scored without the defensive mishap. If a pitcher exits a game with runners on base, any earned runs scored by those runners will count against him.

Earned Run Average (ERA)

Earned run average represents the number of earned runs a pitcher allows per nine innings -- with earned runs being any runs that scored without the aid of an error or a passed ball. ERA is the most commonly accepted statistical tool for evaluating pitchers.

Double Play (DP)

A double play occurs when two offensive players are ruled out within the same play. It's often referred to as "a pitcher's best friend" because it's twice as helpful toward his cause as any given out.

Double (2B)

A batter is credited with a double when he hits the ball into play and reaches second base without the help of an intervening error or attempt to put out another baserunner.

Doctoring the Baseball

No player is permitted to intentionally damage, deface or discolor the baseball by rubbing it with any type of foreign item or substance, including dirt or saliva. Failure to follow this rule will result in an ejection and an automatic 10-game suspension.

Distance Covered (DCOV)

Distance Covered represents the total distance covered by a defender from the time the bat makes contact with the ball until the moment he fields it. This metric only takes into account the route actually traveled by the fielder -- NOT the direct route from the fielder's starting position to the ball. (In fact, if you divide a player's optimal route to the ball by his Distance Covered, you get another Statcast metric called "Route Efficiency.")

Designate for Assignment (DFA)

When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster. Within seven days of the transaction (had been 10 days under the 2012-16 Collective Bargaining Agreement), the player can either be traded or placed on irrevocable outright waivers.

Designated Hitter Rule

The designated hitter rule allows teams to use another player to bat in place of the pitcher. Because the pitcher is still part of the team's nine defensive players, the designated hitter -- or "DH" -- does not take the field on defense.

Designated Hitter

The designated hitter -- or "DH" -- is a player who bats in place of the pitcher. The pitcher still handles his regular duties when his team is on defense, so the designated hitter does not play in the field.

Defensive Runs Saved (DRS)

DRS quantifies a player's entire defensive performance by attempting to measure how many runs a defender saved. It takes into account errors, range, outfield arm and double-play ability. It differs only slightly from UZR (Ultimate Zone Rating) in its formula, but the concept is the same.

Defensive Efficiency Ratio (DER)

Defensive Efficiency Ratio is a statistic used to evaluate team defense by finding out the rate of times batters reach base on balls put in play. Basically, for every ball hit into the field of play, how likely is the defense to convert that into an out?

Dead Ball

A dead ball is a ball that is out of play. The ruling of a dead ball halts the game and no plays can legally occur until the umpire resumes the game, though baserunners can advance as the result of acts that occurred while the ball was live. Dead balls are frequent occurrences during a game, and the dead-ball period typically does not last long before the ball is put back into play.

Cutter (FC)

A cutter is a version of the fastball, designed to move slightly away from the pitcher's arm-side as it reaches home plate. Cutters are not thrown by a large portion of Major League pitchers, but for some of the pitchers who possess a cutter, it is one of their primary pitches.

Curveball (CU)

A curveball is a breaking pitch that has more movement than just about any other pitch. It is thrown slower and with more overall break than a slider, and it is used to keep hitters off-balance. When executed correctly by a pitcher, a batter expecting a fastball will swing too early and over the top of the curveball.

Contract Tendered

To "tender" a contract to a player is to agree to give a contract for the upcoming season to a player who is under club control. Players on the 40-man roster with fewer than six years of Major League service time must be tendered contracts or they will be considered "non-tendered" and immediately made eligible for free agency. Contracts must be tendered to both arbitration-eligible and pre-arbitration players, though the latter group has no say in its forthcoming salary.

Contract Renewal

Players who haven't signed a long-term contract extension or accrued the MLB service time necessary to be eligible for salary arbitration can have their contracts renewed by their clubs as one-year deals for the coming season.

Complete Game (CG)

A pitcher earns a complete game if he pitches the entire game for his team regardless of how long it lasts. If the game is shortened by rain or if it lasts into extra innings, it counts as a complete game if the pitcher was the only pitcher to record an appearance for his team.

Competitive Balance Tax

Each year, clubs that exceed a predetermined payroll threshold are subject to a Competitive Balance Tax -- which is commonly referred to as a "luxury tax." Those who carry payrolls above that threshold are taxed on each dollar above the threshold, with the tax rate increasing based on the number of consecutive years a club has exceeded the threshold.

Competitive Balance Draft Picks

Competitive Balance Draft picks were implemented in the 2012-16 Collective Bargaining Agreement. The process to assign picks was amended in the 2017-21 Collective Bargaining Agreement.

Collisions at Home Plate

The baserunner is not allowed to deviate from his direct path to initiate contact with the catcher (or any player covering the plate). Runners are considered to be in violation of this rule if they collide with the catcher in cases where a slide could have been used to avoid the collision. If the umpire determines that the runner violated this rule, the runner shall be ruled out and the ball is dead. The other runners must return to the last base they had touched at the time of the collision.

Coach Interference

If a base coach interferes with a thrown ball, the runner will be ruled out. But if a thrown ball accidentally touches the base coach, the ball is alive and in play. Coaches must respect the fielder's right of way to make a play on a batted or thrown ball.

Club Option

A club option is an optional year at the end of the contract which may be guaranteed at the discretion of the club. In most instances, the option comes with a buyout that represents a fraction of the option value. If the player is injured or performs on a level that the club believes the option value to be too expensive, the club will typically pay the buyout and decline the option. In most cases, this results in the player being eligible for free agency. However, if a player signed a contract that turned one of his arbitration-eligible seasons into an option season, the option can be declined with the player then entering the arbitration process instead.


Closers stand on the pitching mound, which is located in the center of the infield and 60 feet, six inches away from home plate.

Chin Music

"Chin music" refers to a pitch that is thrown high and inside, near a batter's head.

Changeup (CH)

A changeup is one of the slowest pitches thrown in baseball, and it is predicated on deception.

Center Fielder

The center fielder covers the middle portion of the outfield (when viewing the field from home plate).


The "cellar" refers to last place.

Caught Stealing (CS)

A caught stealing occurs when a runner attempts to steal but is tagged out before reaching second base, third base or home plate. This typically happens after a pitch, when a catcher throws the ball to the fielder at the base before the runner reaches it. But it can also happen before a pitch, typically when a pitcher throws the ball to first base for a pickoff attempt but the batter has already left for second.

Catcher Interference

The batter is awarded first base if the catcher (or any other fielder) interferes with him at any point during a pitch.

Catcher Framing

Catcher framing is the art of a catcher receiving a pitch in a way that makes it more likely for an umpire to call it a strike -- whether that's turning a borderline ball into a strike, or not losing a strike to a ball due to poor framing. The effects of a single pitch can be huge; in 2019, hitters had an .858 OPS after a 1-0 count, but just a .631 OPS after an 0-1 count.


The catcher crouches directly behind home plate and is primarily responsible for receiving all of a pitcher's pitches.

Cape Cod Baseball League

The Cape Cod Baseball League is a prestigious collegiate summer league in Massachusetts that has played host to more than 1,250 future Major Leaguers over the years.

Can of Corn

A "can of corn" is a routine fly ball hit to an outfielder.

Butcher Boy

A "butcher boy" is a batter who squares around to bunt, only to pull the bat back and make a short, downward swing.

Bush League

"Bush league" describes something that is below professional standards.

Bursitis/Shoulder Bursitis

A bursa is a small, fluid-filled sac that serves to reduce friction between a bone and the surrounding soft tissues such as skin, muscles, ligaments and tendons. There are 160 bursae in the body, with the major bursae located in the large shoulder, hip, elbow and knee joints. Bursitis is the inflammation of a bursa.

Bullpen Coach

The bullpen coach works with pitchers in a similar capacity to the pitching coach before and after games. During a game, the bullpen coach is in the bullpen with his club's relief pitchers and oversees their warmups, while also offering advice on pitching mechanics and pitch selection.

Bone Bruise

A bone bruise is a traumatic injury to a bone that is less severe than a bone fracture, causing blood and fluid to build up near the injured bone.


A Bolt is any run where the Sprint Speed (defined as "feet per second in a player's fastest one-second window") of the runner is at least 30 ft/sec.

Blown Save (BS)

A blown save occurs when a relief pitcher enters a game in a save situation, but allows the tying run to score. The run does not have to be charged to that pitcher. If a reliever enters with a man already on third base, and he allows that runner to score the tying run, he is charged with a blown save.

Bequeathed Runners Scored (BQR-S)

Bequeathed runners scored represents the total number of runs a pitcher is charged with after he leaves the game. Or, put another way, it's the number of runners who come around to score after being left on base when that pitcher exits the game.

Bequeathed Runners (BQR)

Bequeathed runners represents the number of runners left on base by a pitcher when that pitcher leaves the game. Any bequeathed runner who scores an earned run after a pitcher has left the game will be counted against that pitcher's ERA.

Bench Coach

A bench coach is typically considered the right-hand man to his team's manager. Bench coaches assist their managers in decision-making and will sometimes relay scouting information from the team's front office to the club's players.

Batting Out of Turn

If a team bats out of turn, the onus is not on the umpires to notify either team of the transgression. The consequences of batting out of turn vary depending on the timing of the appeal.

Batting Average on Balls in Play (BABIP)

BABIP measures a player's batting average exclusively on balls hit into the field of play, removing outcomes not affected by the opposing defense (namely home runs and strikeouts).

Batting Average (AVG)

One of the oldest and most universal tools to measure a hitter's success at the plate, batting average is determined by dividing a player's hits by his total at-bats for a number between zero (shown as .000) and one (1.000). In recent years, the league-wide batting average has typically hovered around .250.

Batters Faced (BF)

Batters faced is simply a count of the number of total plate appearances against a certain pitcher or team. In a perfect game -- with 27 outs -- a pitcher will record 27 batters faced.

Batter's Box

A regulation baseball field has two batter's boxes -- one on the left side and one on the right side of home plate -- drawn using the same chalk as the baselines. From the pitcher's point of view, left-handed batters stand in the batter's box on the left side of the plate and right-handed batters stand in the batter's box on the right side of the plate.


Batters stand a few inches to the right or left of home plate and attempt to put the ball in play against an opposing pitcher. Right-handed batters stand on the third-base side of home plate, and left-handed batters situate toward the first-base side of the plate.

Batted Ball Event (BBE)

A Batted Ball Event represents any batted ball that produces a result. This includes outs, hits and errors. Any fair ball is a Batted Ball Event. So, too, are foul balls that result in an out or an error.

Baserunners Per Nine Innings Pitched (MB/9)

Baserunners per nine innings pitched tells us the average number of baserunners allowed by a pitcher for every nine innings pitched. For the purpose of this statistic, "baserunners" include men who reach on hits, walks and hit-by-pitches. Errors and fielder's choices do not count.


Baserunners stand on or close to first base, second base and third base at the time a pitch is thrown. Once the pitch is thrown, baserunners can try to advance to the next base -- on a stolen-base attempt or after the ball is put into play. The ultimate goal of a baserunner is to score.

Baseball Age (Seasonal Age)

A player's baseball age indicates how old he is as of July 1 in a given season.


The Barrel classification is assigned to batted-ball events whose comparable hit types (in terms of exit velocity and launch angle) have led to a minimum .500 batting average and 1.500 slugging percentage since Statcast was implemented Major League wide in 2015.

Baltimore Chop

A "Baltimore chop" is a chopper that takes a high bounce near home plate, allowing the runner to reach first safely.

Ballpark Factor

Ballpark factor, at its most basic, takes the runs scored by Team X (and its competitors) in Team X's home ballpark and divides the figure by the runs scored by Team X and its competitors in Team X's road contests. Often times, that number will be ever-so-slightly adjusted if a team doesn't play the same opponents at home as on the road.

Balk (BK)

A balk occurs when a pitcher makes an illegal motion on the mound that the umpire deems to be deceitful to the runner(s). As a result, any men on base are awarded the next base, and the pitch (if it was thrown in the first place) is waved off for a dead ball.

Automatic Runner

As part of MLB's health and safety protocols during the COVID-19 pandemic, all half-innings after the ninth will begin with a runner on second base in the 2020 regular season. This rule will not be in place for the 2020 postseason or the 2021 campaign.

At-bat (AB)

An official at-bat comes when a batter reaches base via a fielder's choice, hit or an error (not including catcher's interference) or when a batter is put out on a non-sacrifice. (Whereas a plate appearance refers to each completed turn batting, regardless of the result.)

Assist (A)

An assist is awarded to a fielder who touches the ball before a putout is recorded by another fielder. Typically, assists are awarded to fielders when they throw the ball to another player -- but a fielder receives an assist as long as he touches the ball, even if the contact was unintentional. For example, on a line drive that strikes the pitcher before caroming to the shortstop, both the pitcher and shortstop are awarded an assist if the out is made on a throw to first base.


"Around-the-horn" describes a ground-ball double or triple play that starts with the third baseman and involves a throw to second followed by a throw to first.

Arm Strength (ARM)

Arm Strength is defined as the maximum velocity of any throw made by a fielder -- with the max velocity always being at the release point, due to physics. It can be used to evaluate outfielders on attempted assists, catchers on stolen base and pickoff throws, and infielders on throws across the diamond. Fielders -- especially outfielders -- often get a running start before throwing. As a result, the velocity on their throws can exceed that of pitchers, who throw to batters from the mound.

Appearance (App)

A pitcher is credited with an appearance if he pitches in a given game. When a pitcher enters the game -- barring an injury while warming up -- he must face at least one batter. When crediting pitchers with an appearance, it does not matter whether the pitcher started the game or pitched in relief.

Appeal Plays

The defensive team can appeal certain plays to alert the umpires of infractions that would otherwise be allowed without the appeal. Appeal plays are not the same as a manager asking the umpire for an instant-replay review.

Ambidextrous Pitchers

A pitcher must visually indicate with which hand he will use to pitch prior to the start of a plate appearance. This can be accomplished simply by wearing his glove on his non-throwing hand and placing his foot on the pitching rubber. Barring injury, he is not permitted to pitch with the other hand until the batter is retired, becomes a baserunner or is removed for a pinch-hitter.

All-Star Ballot

All-Star Game starters (except for starting pitchers and the National League's starting designated hitter) are chosen via fan vote, which is broken up into two periods (as of 2019).

Adjusted Earned Run Average (ERA+)

ERA+ takes a player's ERA and normalizes it across the entire league. It accounts for external factors like ballparks and opponents. It then adjusts, so a score of 100 is league average, and 150 is 50 percent better than the league average.

Active Spin

Statcast refers to the spin that contributes to movement as Active Spin.


"Ace" typically refers to a team's No. 1 pitcher, though it can also be used to describe an elite pitcher in general. Therefore, a team with multiple elite pitchers is said to have more than one ace.