Glossary
Every stat on the site, one sentence each. Each entry links to the lesson that teaches it properly.
Level 0 — The stats you already know
Hits divided by at-bats — ignores walks entirely and treats a single like a home run.
great .310 · avg .248 · poor .215
Total home runs — a real skill, but a counting stat that grows with playing time.
great 40+ · avg 18 · poor <8
Runs your hits drove home — depends heavily on how often teammates are on base ahead of you.
great 110+ · avg 65 · poor <40
Times you crossed the plate — needs teammates to drive you in, so it's team-context heavy.
Bags stolen — useful, but without the caught-stealing count it can hide a net negative.
Credited to one pitcher per team win by arcane rules — mostly measures your offense's run support.
Earned runs allowed per 9 innings — polluted by defense, ballpark, and bullpen luck.
great 2.90 · avg 4.10 · poor 5.00+
Plays made without an error — punishes rangy defenders who reach balls others never touch.
Level 1 — Rates, not counts
How often you avoid making an out — counts walks and HBP, which AVG ignores.
great .390 · avg .317 · poor .290
Total bases per at-bat — rewards extra-base power that AVG treats the same as a single.
great .550 · avg .411 · poor .350
SLG minus AVG — pure extra-base power with the singles stripped out.
great .250 · avg .163 · poor .100
OBP + SLG — a quick-and-dirty overall hitting number that slightly undervalues getting on base.
great .900 · avg .728 · poor .650
Strikeouts per plate appearance (or per batter faced) — the honest version of K/9.
great hitter <14% / pitcher >28% · avg 22% · poor hitter >30% / pitcher <18%
Walks per plate appearance — plate discipline for hitters, command for pitchers.
great hitter >13% / pitcher <5.5% · avg 8.5% · poor hitter <4% / pitcher >10%
K% minus BB% — one of the fastest-stabilizing signals of a pitcher's true skill.
great 20%+ · avg 13% · poor <8%
Baserunners allowed per inning — simple, but blind to whether hits were the defense's fault.
great 1.00 · avg 1.28 · poor 1.45+
Level 2 — Luck, context, and the 100 scale
AVG on balls that stayed in the park — extreme values usually scream luck, not skill.
great — · avg .291 · poor —
How much a ballpark inflates or deflates offense — Coors Field runs ~110, pitcher parks ~95.
OPS adjusted for park and league, scaled so 100 = average and 120 = 20% better than average.
great 150 · avg 100 · poor 80
ERA adjusted for park and league, flipped so higher is better — 100 = average, 130 = excellent.
great 140 · avg 100 · poor 85
Level 3 — Linear weights
The average number of runs an event is worth, measured from millions of real innings — a walk ≈ 0.3, a HR ≈ 1.4.
Total runs a player added or lost versus the average outcome of each base-out situation he faced — clutch context included, summed over the season.
great +40 · avg 0 · poor -15
Like OBP but each way of reaching base is weighted by its real run value — the best single rate stat for hitters.
great .400 · avg .318 · poor .290
wOBA converted to counting form — how many runs a hitter added versus a league-average bat.
great +40 · avg 0 · poor -10
Total hitting value, park- and league-adjusted, on the 100-scale — the number people quote when arguing about hitters.
great 150 · avg 100 · poor 80
An ERA-scaled number built only from strikeouts, walks, and homers — the things a pitcher truly controls.
great 3.00 · avg 4.10 · poor 4.80+
FIP with the pitcher's HR luck replaced by a league-average home-run-per-fly-ball rate.
great 3.20 · avg 4.10 · poor 4.70+
Level 4 — Statcast
How hard the ball leaves the bat, in mph — process, not outcome; luck can't fake it.
great 93+ mph · avg 88.5 mph · poor <86 mph
A hitter's hardest-hit ball of the season — a raw-strength ceiling that stabilizes almost instantly.
great 115+ mph · avg 109 mph · poor <105 mph
The vertical angle the ball leaves the bat — grounders < 10°, line drives 10–25°, flies > 25°.
A batted ball with the EV + launch-angle combo that historically produces at least a .500 AVG and 1.500 SLG.
great 15%+ of BBE · avg 7.5% · poor <4%
Share of batted balls at 95+ mph — the simplest 'is the contact real?' check.
great 50%+ · avg 39% · poor <30%
Share of batted balls launched at 8–32° — the angles where hits actually live.
great 38%+ · avg 33% · poor <28%
What your AVG 'should be' given the EV and launch angle of every ball you hit — defense and luck removed.
great .300 · avg .245 · poor .215
SLG rebuilt from quality of contact instead of actual outcomes.
great .560 · avg .399 · poor .330
The king of expected stats — wOBA rebuilt from contact quality plus real Ks and BBs; large gaps vs wOBA hint at luck.
great .400 · avg .312 · poor .280
Swings that miss, per swing — the purest measure of how hard a pitch is to hit.
great pitcher 30%+ · avg 24% · poor pitcher <18%
Swings at pitches outside the zone — discipline for hitters (lower = better), deception for pitchers (higher = better).
great hitter <22% · avg 28.5% · poor hitter >35%
Ball rotation in rpm — shapes how much a pitch rises, sinks, or sweeps versus gravity's default.
Inches of horizontal and vertical break versus a spinless ball — the geometry that makes pitches miss bats.
Level-3 run values applied pitch by pitch — grades each offering by how outcomes shifted when it was thrown.
Feet per second in a player's fastest one-second window — 30+ is elite, 27 is average, 25 is station-to-station.
great 29+ ft/s · avg 27 ft/s · poor <25.5 ft/s
Range-based defense: outs recorded versus the probability an average fielder makes each play.
great +12 · avg 0 · poor -8
Average mph on a fielder's hardest throws — Statcast measures the cannon directly.
Swing speed at the sweet spot in mph — 75+ is elite power material, ~71 is average.
great 75+ mph · avg 71 mph · poor <68 mph
Level 5 — Total value
The performance of a freely available AAA call-up — the honest zero point for measuring value.
A value bump or penalty by position — an average-hitting shortstop is worth far more than an average-hitting DH.
Batting + baserunning + defense + position, converted to wins versus a replacement player — a framework, not gospel.
great 6+ (MVP-ish) · avg 2 (solid starter) · poor 0 (replacement)
A forecast of true talent: weighted recent seasons, regressed toward the league, adjusted for age — StatLab's version is deliberately simple and fully explained.
How much each play moved the team's chance of winning — great for storytelling, unreliable for judging talent.
How much the current situation can swing the game — 1.0 is average, 2+ is white-knuckle time.