Glossary

Rate and counting stats that describe a hitter's production at the plate.

AVGBatting Average

Hits divided by at-bats. The oldest headline hitting stat, but it ignores walks and treats every hit as equal.

OBPOn-Base Percentage

How often a hitter reaches base via hit, walk, or hit-by-pitch, per plate appearance. Captures the plate discipline that AVG misses.

SLGSlugging Percentage

Total bases per at-bat. Weights extra-base hits so it reflects power, not just how often a batter reaches.

OPSOn-Base Plus Slugging

OBP plus SLG. A quick, single-number blend of getting on base and hitting for power; roughly .800 is good, .900+ is excellent.

OPS+Adjusted OPS

OPS scaled to league and park so 100 is league average and each point above/below is one percent better/worse than average.

ISOIsolated Power

SLG minus AVG — extra bases per at-bat. Strips singles out of slugging to isolate raw power.

BABIPBatting Average on Balls in Play

How often batted balls (excluding home runs) fall for hits. Extreme values often signal luck that regresses toward a hitter's norm.

wOBAWeighted On-Base Average

An all-in-one rate stat that weights each outcome (walk, single, double, HR…) by its real run value. Scaled to look like OBP.

wRC+Weighted Runs Created Plus

Total offensive value adjusted for park and league, where 100 is average and 150 means 50% better than average.

BB%Walk Rate

Walks as a share of plate appearances. A core plate-discipline indicator for hitters.

K%Strikeout Rate

Strikeouts as a share of plate appearances. Lower is generally better for a hitter.

Batted-ball tracking data and the expected outcomes derived from exit velocity and launch angle.

EVExit Velocity

How fast the ball leaves the bat, in mph. Higher exit velocity correlates strongly with better outcomes.

LALaunch Angle

The vertical angle the ball leaves the bat. Line drives and productive fly balls generally sit in the ~8–32° range.

Barrel%Barrel Rate

Share of batted balls that are 'barrels' — the exit-velocity/launch-angle combos that historically produce the best results (min ~98 mph in an ideal angle band).

Hard-Hit%Hard-Hit Rate

Share of batted balls hit at 95 mph or harder. A simple, stable proxy for quality of contact.

Sweet Spot%Sweet-Spot Rate

Share of batted balls hit in the 8–32° launch-angle band, where line drives and productive fly balls live.

Max EVMaximum Exit Velocity

A hitter's hardest-hit ball of the season. A ceiling indicator of raw power that stabilizes quickly.

xBAExpected Batting Average

The batting average a hitter 'should' have based on the exit velocity and launch angle of their batted balls, independent of defense and luck.

xSLGExpected Slugging

Expected slugging percentage from batted-ball quality — the SLG the contact profile deserves regardless of where balls landed.

xwOBAExpected Weighted On-Base Average

wOBA estimated from quality of contact (plus real walks and strikeouts). A gap between wOBA and xwOBA often points to luck.

xwOBACONExpected wOBA on Contact

Expected wOBA counting only balls put in play — a pure measure of contact quality that removes walks and strikeouts.

Swing-decision and contact metrics from pitch-level tracking.

Swing%Swing Rate

Share of pitches a batter swings at, in or out of the zone.

Chase%Chase Rate (O-Swing%)

Share of pitches outside the strike zone that a batter swings at. Lower chase rates reflect better discipline.

Zone%Zone Rate

Share of pitches thrown inside the strike zone. For pitchers, a marker of how aggressively they attack.

Contact%Contact Rate

Share of swings that make contact with the ball.

Whiff%Whiff Rate

Swings and misses as a share of total swings. High whiff rates for pitchers signal swing-and-miss stuff.

SwStr%Swinging-Strike Rate

Swings and misses as a share of all pitches (not just swings). A reliable early indicator of a pitcher's strikeout ability.

CSW%Called Strikes + Whiffs

Called strikes plus swinging strikes as a share of total pitches. Combines command and stuff into one strike-generation number.

F-Strike%First-Pitch Strike Rate

Share of plate appearances that begin with a strike. Getting ahead 0-1 tilts the count heavily in the pitcher's favor.

Run-prevention and rate stats that describe a pitcher's results and skills.

ERAEarned Run Average

Earned runs allowed per nine innings. The headline pitching stat, but heavily influenced by defense and sequencing luck.

FIPFielding Independent Pitching

An ERA-scaled estimate built only from strikeouts, walks, hit-by-pitches, and home runs — the outcomes a pitcher most controls.

xFIPExpected FIP

FIP that replaces a pitcher's actual home runs with a league-average rate on their fly balls, smoothing out HR luck.

WHIPWalks + Hits per Inning Pitched

Baserunners allowed (walks plus hits) per inning. A quick read on how often a pitcher lets runners on.

BAABatting Average Against

Opponent hits divided by opponent at-bats. It shows how often hitters record a hit against a pitcher, with lower values indicating better hit suppression.

K/9Strikeouts per Nine

Strikeouts per nine innings pitched — a rate view of missing bats.

BB/9Walks per Nine

Walks allowed per nine innings pitched — a rate view of control.

K/BBStrikeout-to-Walk Ratio

Strikeouts divided by walks. A durable measure of a pitcher's command-plus-stuff profile.

HR/9Home Runs per Nine

Home runs allowed per nine innings pitched.

LOB%Left On-Base Rate

Share of baserunners a pitcher strands. Extreme values tend to be unsustainable and regress toward league average (~72%).

ERA-Adjusted ERA (ERA Minus)

ERA scaled to league and park where 100 is average and lower is better — 90 means 10% better than average.

Tracking measurements that describe the shape and quality of individual pitches.

VeloVelocity

Pitch speed in mph, typically measured just out of the pitcher's hand.

Spin RateSpin Rate

How fast a pitch spins, in rpm. Combined with spin axis, it helps explain a pitch's movement.

IVBInduced Vertical Break

Vertical movement from spin alone, with gravity removed. High IVB four-seamers appear to 'rise' and generate whiffs up in the zone.

HBHorizontal Break

How much a pitch moves side-to-side, in inches, relative to a spinless path.

ExtensionRelease Extension

How far in front of the rubber a pitcher releases the ball. More extension makes velocity 'play up' by shortening the batter's reaction time.

Stuff+Stuff Plus

A model grade of a pitch's raw physical quality (velocity, movement, release), where 100 is average and higher is nastier.

Defensive value, arm and range tracking, and baserunning speed.

OAAOuts Above Average

A range-based defensive metric counting how many outs a fielder makes above or below what an average fielder would, given each play's difficulty.

DRSDefensive Runs Saved

An all-encompassing defensive metric estimating runs a fielder saves or costs versus average across range, arm, and more.

UZRUltimate Zone Rating

A zone-based estimate of the runs a fielder saves or costs relative to average, primarily through range and errors.

Sprint SpeedSprint Speed

A runner's top speed in feet per second on qualifying plays. ~27 ft/s is average; 30+ is elite.

Arm StrengthArm Strength

The average velocity of a fielder's throws, in mph.

Pop TimePop Time

For catchers, the time in seconds from the pitch hitting the mitt to the throw reaching the base on a steal attempt.

Summary value metrics and the adjustments that make stats comparable.

WARWins Above Replacement

A single estimate of a player's total value — hitting, fielding, baserunning, pitching — in wins over a freely available replacement-level player.

Park FactorPark Factor

How much a ballpark inflates or suppresses a stat versus a neutral park. 100 is neutral; above 100 favors that outcome.

PercentilePercentile Rank

Where a player ranks among qualified peers, 0–100. A 90th-percentile mark means the player is better than 90% of the field.