Baseball Glossary

Position 3. Receives throws from infielders and typically fields balls hit to the right side.

Example: First basemen are often power hitters with good hands.

Position 4. Covers second base and the area between first and second.

Example: Second basemen turn double plays and need quick hands.

Position 5. Called the "hot corner" because of hard-hit balls down the line.

Example: Third basemen need quick reactions and a strong arm.

Credited to a fielder who throws or touches the ball before a putout is recorded.

Example: A shortstop throwing to first gets an assist on the groundout.

An official plate appearance that counts toward batting average. Excludes walks, HBP, sacrifices, and interference.

Example: A player has an at-bat when they hit, strike out, or reach on an error.

Maximum throwing velocity for position players, typically measured on throws to bases.

Example: Elite outfielders can throw 95+ mph.

The ratio of hits to at-bats. Calculated by dividing hits by at-bats. A .300 average is considered excellent.

Example: A player with 150 hits in 500 at-bats has a .300 batting average.

Batting average on balls hit into the field of play, excluding home runs and strikeouts. League average is around .300.

Example: A high BABIP may indicate luck or skill; very high/low tends to regress.

An illegal pitching motion that results in all baserunners advancing one base.

Example: Coming set improperly or faking a throw to first can be a balk.

A batted ball with ideal exit velocity and launch angle combination, resulting in .500+ BA and 1.500+ SLG historically.

Example: Barrels are the most damaging batted balls.

When a batter receives four balls and is awarded first base.

Example: A patient hitter with good plate discipline will draw many walks.

Average number of walks a pitcher allows per nine innings. Lower is better. Sub-2.5 is good.

Example: A pitcher with excellent control will have a low BB/9.

When a pitcher enters a save situation and allows the tying run to score.

Example: A closer who allows a 9th-inning lead to vanish gets a blown save.

WAR calculated by Baseball-Reference, using RA9 for pitchers and DRS for defense.

Example: bWAR is also called rWAR (reference WAR).

Position 2. Receives pitches, calls the game, and guards home plate.

Example: The catcher is the only player who faces the entire field.

The likelihood that a fielder will make a catch, based on distance and time to the ball.

Example: A 5-star catch has less than 25% catch probability.

Position 8. The most important outfield position, requiring the most range.

Example: Center fielders are typically the fastest and best defensive outfielders.

When a starting pitcher pitches the entire game without being replaced.

Example: Complete games are increasingly rare in modern baseball.

The relief pitcher who typically pitches the 9th inning to preserve a lead and earn saves.

Example: Closers are judged by saves and blown saves.

When a baserunner attempting to steal is tagged out before reaching the next base.

Example: A good base stealer should be caught less than 25% of the time.

Percentage of baserunners thrown out attempting to steal. Good catchers are above 30%.

Example: Elite catchers can throw out 40%+ of base stealers.

When a batter hits a single, double, triple, and home run in the same game.

Example: The triple is usually the hardest part of hitting for the cycle.

A player who bats in place of the pitcher. Used in both leagues since 2022.

Example: The DH allows pitchers to focus solely on pitching.

When the defense records two outs on the same play.

Example: The 6-4-3 (SS to 2B to 1B) is the most common double play.

Estimates runs saved (or cost) by a fielder compared to average. Zero is average; positive is better.

Example: A +15 DRS means the fielder saved 15 runs above average.

A misplay that prolongs a batter's at-bat or allows a runner to advance when they should have been out.

Example: Dropping a routine fly ball is scored as an error.

The average number of earned runs a pitcher allows per nine innings. Lower is better. Sub-3.00 is excellent.

Example: A pitcher with 30 earned runs in 150 innings has a 1.80 ERA.

ERA adjusted for ballpark and league. 100 is league average; higher is better. 150+ is elite.

Example: An ERA+ of 150 means 50% better than league average.

The speed of the ball off the bat, measured in mph. Higher exit velocity correlates with better offensive results.

Example: Balls hit 95+ mph are considered "hard hit."

How far toward home plate a pitcher releases the ball. More extension means less reaction time.

Example: Pitchers with 7+ feet of extension have an advantage.

Measures what a pitcher's ERA should be based on strikeouts, walks, HBP, and home runs, removing fielding.

Example: FIP isolates a pitcher's performance from their defense.

Percentage of plays a fielder makes without an error. Higher is better, though it ignores range.

Example: A .990 fielding percentage means an error about once every 100 chances.

A catcher's ability to receive pitches in a way that increases called strikes.

Example: Good framers can add several wins per season for their pitchers.

WAR calculated by FanGraphs, using FIP for pitchers and UZR for defense.

Example: fWAR and bWAR may differ slightly due to methodology.

When a batter hits a ground ball that results in two outs.

Example: Slow runners ground into more double plays.

Ratio of ground ball outs to fly ball outs. Ground ball pitchers have higher ratios.

Example: Sinkerball pitchers typically have GO/AO above 1.5.

A fair ball that bounces into the stands or becomes unplayable. Batter gets second base.

Example: A ball bouncing over the outfield wall is a ground rule double.

When a batter reaches base safely due to a batted ball, without an error or fielder's choice.

Example: Singles, doubles, triples, and home runs are all hits.

Percentage of batted balls with exit velocity of 95+ mph.

Example: A 45%+ hard hit rate is excellent.

When a pitched ball hits the batter and they are awarded first base.

Example: Some batters crowd the plate and get hit frequently.

Awarded to a reliever who enters with a lead, records at least one out, and leaves with the lead intact without finishing.

Example: Setup men earn holds by bridging to the closer.

A hit that allows the batter to round all bases and score, typically by hitting the ball over the outfield fence.

Example: A ball hit over the fence in fair territory is a home run.

Average number of home runs allowed per nine innings. Lower is better. Sub-1.0 is good.

Example: Fly ball pitchers often have higher HR/9 rates.

When a pitcher deliberately walks a batter, now done by manager signal without pitches.

Example: Teams intentionally walk dangerous hitters in key situations.

With runners on first and second (or bases loaded) and less than two outs, a pop fly in the infield is automatically an out.

Example: The rule prevents fielders from deliberately dropping balls for double plays.

The number of innings a pitcher has worked. Each out is one-third of an inning.

Example: 6.2 IP means six full innings plus two outs in the seventh.

Measures raw power by subtracting batting average from slugging percentage. Shows extra-base hit ability.

Example: An ISO of .200+ indicates a power hitter.

Average number of strikeouts a pitcher records per nine innings. Higher is better. 9+ is excellent.

Example: A pitcher with 200 K in 180 IP has a 10.0 K/9.

The ratio of strikeouts to walks. Higher is better. 3.0+ is very good; 4.0+ is elite.

Example: A K/BB of 4.0 means 4 strikeouts for every walk.

Assigned to the pitcher who allows the go-ahead run that the winning team never loses.

Example: A reliever can take the loss if they allow the winning run.

The vertical angle at which the ball leaves the bat. 10-25 degrees is ideal for line drives and home runs.

Example: A launch angle of 25-30 degrees often produces home runs.

Position 7. Outfield position on the left side when facing home plate.

Example: Left fielders often have strong arms for throws to third.

Runners who remain on base when an inning ends without scoring.

Example: High LOB often indicates missed scoring opportunities.

Percentage of baserunners a pitcher strands. League average is around 72%.

Example: An unsustainably high LOB% may indicate future regression.

A left-handed reliever used primarily to face left-handed batters (less common with new rules).

Example: MLB's 3-batter minimum rule reduced LOOGY usage.

A game in which one team records no hits. Walks and errors may still occur.

Example: A no-hitter is one of baseball's rarest achievements.

Statcast metric measuring outs made above or below what an average fielder would make.

Example: OAA uses tracking data for precise defensive evaluation.

Measures how often a batter reaches base. Includes hits, walks, and hit-by-pitches. Higher is better.

Example: A .400 OBP means a player reaches base 40% of plate appearances.

Combines OBP and SLG into one stat that measures overall offensive value. An OPS of .900+ is excellent.

Example: A player with .380 OBP and .520 SLG has a .900 OPS.

OPS adjusted for ballpark and league average. 100 is league average, higher is better. 150+ is elite.

Example: An OPS+ of 150 means 50% better than league average.

Position 1. Throws the ball to the catcher and is the defensive hub.

Example: Pitchers are divided into starters and relievers.

Any completed turn at bat, including walks, hit-by-pitches, and sacrifices. Used for qualifying rates.

Example: To qualify for the batting title, a player needs 3.1 PA per team game.

An error charged to a catcher when they fail to hold a pitch that should have been caught.

Example: A pitch in the dirt that gets by is usually a wild pitch, not a passed ball.

A game in which a pitcher faces the minimum 27 batters with no one reaching base.

Example: Only 24 perfect games have been thrown in MLB history.

A substitute batter who hits for another player in the lineup.

Example: Pinch hitters are often used for pitchers' at-bats.

Credited to a fielder who records an out, either by catching a ball or tagging a runner/base.

Example: First basemen and catchers typically lead in putouts.

A substitute runner who enters the game specifically to run the bases.

Example: Fast pinch runners are used in late-inning situations.

Expected win-loss record based on runs scored and runs allowed.

Example: Teams that outperform their Pythagorean record often regress.

When a starting pitcher completes at least six innings while allowing three or fewer earned runs.

Example: A quality start gives the team a good chance to win.

The number of times a player crosses home plate to score.

Example: A leadoff hitter who scores frequently will have a high runs total.

The number of runs that score as a direct result of a batter's plate appearance (excluding errors and double plays).

Example: A bases-loaded single that scores two runners gives the batter 2 RBIs.

Bill James's formula estimating how many runs a player contributes to their team.

Example: Runs created estimates offensive contribution.

Measures run value of events based on the 24 possible base-out situations.

Example: A grand slam has a higher RE24 than a solo homer.

Average number of putouts and assists per game. Measures how many plays a fielder is involved in.

Example: A high range factor suggests good range, though context matters.

Position 9. Outfield position on the right side, requiring a strong arm for throws to third.

Example: Right fielders need the strongest arms of all outfielders.

When there are baserunners on second and/or third base, within easy scoring distance.

Example: Batting average with RISP measures clutch hitting.

Any pitcher who enters after the starting pitcher. Includes setup men and closers.

Example: Relievers often throw harder for shorter stints.

A bunt where the batter intentionally gives themselves up to advance runners.

Example: Sacrifice bunts are common with a runner on second and no outs.

A fly ball out that allows a runner to tag up and score from third base.

Example: Sacrifice flies don't count as at-bats but do count as RBIs.

When a baserunner advances to the next base while the pitcher delivers the ball, without a hit or error.

Example: A successful stolen base requires speed and timing.

A reliever who typically pitches the 7th or 8th inning to bridge to the closer.

Example: Elite setup men are crucial for getting to the closer.

A complete game in which the pitcher allows no runs.

Example: A shutout is one of pitching's most impressive achievements.

Measures the power of a hitter by calculating total bases per at-bat. Singles = 1, Doubles = 2, Triples = 3, Home Runs = 4.

Example: A .500 SLG means a player averages half a base per at-bat.

When a batter accumulates three strikes and is out. "K" is the traditional scorekeeping symbol.

Example: A backwards K (Ꝁ) indicates a called third strike.

A pitcher who begins the game and typically pitches 5-7 innings.

Example: Teams use a 5-man rotation of starting pitchers.

Revolutions per minute (RPM) on a pitched ball. Higher spin on fastballs creates rise effect.

Example: Elite fastballs spin at 2400+ RPM.

Baserunner's speed measured in feet per second. 30+ ft/s is elite speed.

Example: The fastest players exceed 30 feet per second.

Position 6. The key infield position, covering the area between second and third.

Example: Shortstops need range, arm strength, and quick reflexes.

Awarded to a reliever who finishes a win and meets certain criteria: 3+ innings, tying run on base/at bat/on deck, or 3-run lead.

Example: Closers specialize in earning saves in the 9th inning.

The total number of bases a player has gained from hits. Single=1, Double=2, Triple=3, HR=4.

Example: A player with 300+ total bases is having an excellent offensive season.

A player who both pitches and hits regularly, like Shohei Ohtani.

Example: True two-way players are extremely rare in modern baseball.

A versatile player who can play multiple defensive positions.

Example: Utility players provide lineup flexibility for managers.

Advanced defensive metric measuring runs above/below average based on zone-based analysis.

Example: UZR breaks down defense into range, errors, and double plays.

Awarded to the pitcher of record when their team takes a lead they never relinquish. Starter must pitch 5+ innings.

Example: A starter can get a win even if relievers pitch the final innings.

A game-ending play in the bottom of the final inning where the home team takes the lead.

Example: Walk-off home runs are among baseball's most exciting plays.

Comprehensive stat measuring a player's total value in wins compared to a replacement-level player. 2 is average starter, 5+ is All-Star, 8+ is MVP.

Example: A 6 WAR player is worth about 6 more wins than a minor leaguer.

Measures how many baserunners a pitcher allows per inning. Lower is better. Sub-1.00 is elite.

Example: A WHIP of 1.10 means about one baserunner per inning.

Advanced stat that weights each method of reaching base by its actual run value. More accurate than OPS.

Example: A .400 wOBA is excellent; league average is around .320.

Measures how much a player's actions affected their team's probability of winning.

Example: A walk-off home run adds nearly 50% win probability.

Measures offensive value with 100 as league average. Accounts for park and league factors.

Example: A wRC+ of 130 means 30% better than league average offense.

Batting average a player "should have" based on exit velocity and launch angle of balls in play.

Example: If BA is lower than xBA, the player may be unlucky.

Total of doubles, triples, and home runs. Measures a player's ability to hit for extra bases.

Example: 40+ XBH in a season indicates good power production.

Like FIP but assumes league-average home run rate on fly balls. More predictive than FIP.

Example: xFIP is useful for predicting future performance.

Slugging percentage expected based on quality of contact (exit velocity and launch angle).

Example: xSLG removes fielding and luck from the equation.

Expected wOBA based on exit velocity and launch angle. Removes defense and luck.

Example: xwOBA is one of the best measures of true offensive skill.