Analytics Glossary

The portion of spin that directly affects pitch movement, as opposed to gyroscopic (non-useful) spin.

The angle at which a pitch crosses the plate vertically, affecting how hitters perceive pitch location.

Statcast metric measuring the average velocity of throws by a fielder, measured in miles per hour (mph).

A plate appearance that results in a hit, error, fielder's choice, or out, excluding walks, hit-by-pitches, sacrifice bunts, sacrifice flies, and catcher interference.

Average of available projection systems, often more accurate than individual projections.

Area Under the Receiver Operating Characteristic Curve, measuring classification model performance.

MLB's official Statcast data website, providing access to pitch-level tracking data from 2015-present.

Number of walks a pitcher allows per nine innings, calculated as (BB × 9) / IP.

Walks per plate appearance, calculated as BB / PA × 100. League average is approximately 8-9%.

Runs saved by a catcher blocking pitches in the dirt.

Runs saved by a catcher through pitch framing, turning balls into strikes.

ERA estimator using individual component rates (K, BB, HR, etc.) rather than actual runs.

Percentage of pitches outside the strike zone at which a batter swings, calculated as swings outside zone / pitches outside zone.

A FanGraphs metric measuring how much better or worse a player performed in high-leverage situations.

A swing on a pitch that could reasonably be put in play, used to measure swing decisions.

Percentage of pitches resulting in either a called strike or swinging strike, measuring pure stuff effectiveness.

A fastball variant that breaks slightly toward the pitcher's glove side, combining characteristics of a fastball and slider.

A defensive metric quantifying runs prevented or allowed compared to an average fielder at the same position, used in Baseball Reference's WAR calculation.

Baseball Prospectus's proprietary pitching metric that estimates a pitcher's true run prevention ability based on batted ball and pitch characteristics.

ERA scaled so that 100 is league average, with lower being better. Calculated as (ERA / lgERA) × 100.

The long-term average value of a bet, calculated as (Prob × Win) - ((1-Prob) × Loss).

FIP scaled so that 100 is league average, with lower being better. Calculated as (FIP / lgFIP) × 100.

Percentage of plate appearances starting with a strike.

The standard fastball grip with all four seams rotating, typically the pitcher's highest velocity pitch with backspin-induced rise.

Percentage of batted balls classified as ground balls, calculated as GB / Balls in Play. League average is approximately 45%.

Average leverage index when a player entered games.

Spin that rotates around the direction of travel (like a football spiral), providing little movement but affecting perception.

Percentage of fly balls that become home runs. League average is typically 12-14%.

Horizontal movement of a pitch from the pitcher's perspective, measured in inches.

Number of home runs a pitcher allows per nine innings, calculated as (HR × 9) / IP.

Vertical movement of a pitch relative to a theoretical spinless pitch, accounting for gravity.

The number of outs recorded by a pitcher divided by three, with partial innings represented as .1 (1 out) or .2 (2 outs).

Hall of Fame metric averaging career WAR with 7-year peak WAR, compared to position average.

Number of strikeouts a pitcher records per nine innings, calculated as (K × 9) / IP.

Ratio of strikeouts to walks, calculated as K / BB. League average for pitchers is approximately 2.5-3.0.

Strikeouts per plate appearance, calculated as K / PA × 100. League average for batters is approximately 22-23%, for pitchers approximately 22%.

ERA estimator based solely on strikeout and walk rates, useful as a quick-and-dirty ERA predictor.

Percentage of batted balls classified as line drives, calculated as LD / Balls in Play. League average is approximately 20%.

The distance a baserunner takes from the base before a pitch is delivered, measured in feet.

Measure of game situation importance, with 1.0 being average. High-leverage situations have LI > 1.5.

A system for assigning run values to different offensive events (singles, doubles, walks, etc.) based on their impact on run scoring.

Percentage of baserunners who do not score, calculated as (H + BB + HBP - R) / (H + BB + HBP - 1.4×HR). League average for pitchers is approximately 72%.

Model-based metric measuring the quality of pitch location relative to optimal targets.

Average absolute difference between predictions and actual values.

Percentage of pitches outside the strike zone at which a batter swings. League average is approximately 30%.

Statcast's primary defensive metric, quantifying runs prevented above an average fielder based on catch probability and successful plays.

A metric quantifying how much a ballpark influences run scoring, with 100 being neutral, >100 favoring hitters, and <100 favoring pitchers.

Baseball Prospectus metric estimating ERA based on underlying pitch characteristics.

The effective velocity of a pitch accounting for release extension, giving the batter's perceived speed at release.

The skill of a catcher in receiving pitches to influence umpire strike calls, typically measured in runs added or strikes gained.

Run value of each pitch type thrown by a pitcher, based on outcomes and context.

Wins component attributed to pitching in win probability models.

Component of WAR measuring runs prevented or allowed from pitching, relative to average.

Combined metric incorporating Stuff+, Location+, and pitch sequencing.

Performance difference when facing same-handed vs opposite-handed pitchers/batters.

Average leverage index for all situations faced by a pitcher.

Time from when the pitch hits the catcher's mitt to when the throw reaches second base on a steal attempt, measured in seconds.

Percentage of two-strike pitches that result in a strikeout.

The number of runs a player contributes above a league-average player, before adjustments for position and replacement level.

Runs above average based on the 24 base-out states, measuring situational production.

The tendency for extreme performances to move toward average over time.

The expected performance level of a player who could be readily acquired from the minor leagues or free agency, approximately 20 runs below average per 600 PA.

The average number of runs expected to score in an inning given a specific base-out state.

Movement generated by the orientation of seams disrupting airflow asymmetrically, independent of Magnus force.

Additional distance gained by a baserunner after the pitch is delivered but before a play is made.

An ERA estimator that accounts for strikeouts, walks, ground balls, and their interactions, designed to predict future ERA better than FIP.

A breaking pitch with tight spin and late break, typically breaking glove-side and down from the pitcher's perspective.

The direction of a pitch's spin represented as a clock face from the catcher's perspective, measured in degrees from 0-360.

Percentage of a pitch's total spin that contributes to movement, excluding gyroscopic spin.

The rate at which a baseball rotates while in flight, measured in revolutions per minute (rpm). Higher spin rates typically create more movement.

Statcast metric measuring a player's feet-per-second rate on competitive plays, such as home-to-first on ground balls. League average is approximately 27 ft/s.

MLB's advanced tracking technology that measures player movements, pitch characteristics, and batted ball data using high-resolution cameras and radar.

Model-based metric predicting strikeout rate based purely on pitch characteristics (velocity, movement, etc.).

Percentage of all pitches that result in swinging strikes, calculated as swinging strikes / pitches. League average is approximately 11%.

ERA estimator from StatCorner accounting for batted ball types and sequencing.

The location where two different pitch types are visually indistinguishable to the batter, typically 20-25 feet from home plate.

Fastball grip showing two seams in rotation, typically with more arm-side movement and slightly lower velocity than a four-seamer.

Baserunning value from non-stolen base events: advancing on hits, sac flies, wild pitches, etc.

Percentage of total pitches that are a specific pitch type.

Defensive metric dividing the field into zones and measuring a fielder's effectiveness in each zone compared to the league average, measured in runs.

The angle at which a pitch crosses the plate relative to the ground, measured in degrees. Flatter angles (closer to 0) are generally harder to hit.

Run value above average for all curveballs thrown.

Run value above average for all changeups thrown.

Run value above average for all fastballs thrown, per 100 pitches scaled.

Number of baserunners allowed per inning, calculated as (BB + H) / IP. League average is approximately 1.30.

Win Probability Added divided by average leverage, showing performance independent of situation.

Run value above average for all sliders thrown.

FIP calculated using league average HR/FB rate instead of actual HR/FB, designed to remove luck from home run outcomes.

Percentage of swings on pitches in the zone that result in contact. League average is approximately 85%.

Percentage of pitches in the strike zone at which a batter swings. League average is approximately 68%.

Percentage of pitches thrown inside the strike zone, calculated as pitches in zone / total pitches. League average is approximately 45%.