Glossary
What every number on this site is, and what it is not.
Descriptive — not a forecastExport 2026-10-26
Grades
100 = MLB average, higher is better, clipped to [50, 175]. Every grade on this site is descriptive.
- Stuff+
- Per pitch class × batter side, from Hawk-Eye kinematics only: velocity, induced break, horizontal break, spin, release (height/side/extension), velocity and break differentials from the pitcher's other pitches, hvaa (approach angle), spin efficiency (per-class monotone), and a velocity × induced-break interaction. 6 LightGBM models (class FB/BB/CH × batter side), trained 2023–24 on CSW rate normalized by count.
- ABStuff+
- The same predictions on one scale across all pitch types (a single league reference), so a fastball 95 and a slider 95 mean the same thing.
- Pitching+
- Stuff plus where he threw it: the same model family with plate location and count features added, still per class × side. Like Stuff+, descriptive.
- Descriptive, not a forecast
- Grades describe this season's stuff and run prevention. They are not forecasts: on clean season pairs the model has not beaten naive persistence (RESULTS-MLB §13), so nothing here projects next season. The model card carries
gate_status: descriptive-only— set by the evidence in RESULTS-MLB (the location check passed; predictiveness vs naive persistence is mixed). Nothing on this site projects next season. - Confidence
- Pitch-count floors on the graded sample: HIGH ≥ 400 pitches, MODERATE ≥ 150, LOW ≥ 50, MINIMAL below that.
- One grade, two rows
- Types are graded by class: four-seamers, sinkers and cutters share the FB grade; breaking balls share BB; changeups and splitters share CH. Profiles show the note when two rows carry the same number, and per-type percentile chips rank the shared grade within the type.
Rates and raw stats
Computed from public Statcast day files; no model involved.
- K% / BB% / K-BB%
- Strikeouts, walks and their difference as a share of batters faced.
- CSW%
- Called strikes plus all whiffs (swinging and foul-tip), over taken pitches — the rate the stuff model is trained against.
- Whiff%
- Swinging strikes (including foul tips and blocked swings) over swings.
- Zone% / Chase%
- Pitches in the zone over total; out-of-zone swings over out-of-zone pitches.
- RA/9 (era)
- Runs allowed per nine innings — earned and unearned, deliberately, because pitcher responsibility for sequencing is part of what “runs” means.
- FIP
- Fielding-independent pitching: (13·HR + 3·BB − 2·K) / IP + constant. Standard FanGraphs construction.
- GB%
- Ground balls over balls in play, per pitch class on profiles.
- IVB / HB
- Induced vertical break and horizontal break from Hawk-Eye, inches. HB is signed in Statcast's convention; the movement plot labels the pitcher's arm side.
- VAA
- Vertical approach angle at the plate, from the release kinematics. Profiles show it by zone cell (height × arm side).
- Arm° / slot bands
- Release angle from the mound: 0° sidearm, 90° over the top, banded (over the top, high ¾, ¾, low ¾, sidearm, submarine).
Savant reference boards
Attributed public data, shipped as-is under the descriptive label.
- What these are
- Baseball Savant's published leaderboard tables — bat tracking, expected statistics, swing/take, outs above average, fielding run value, sprint speed, catcher framing/blocking/throwing — re-published here as reference boards with attribution. They are Savant's numbers, not ours, and they are not our models' validation even where a future model will be checked against them.
- Why they are here
- The MVP has no hitter leaderboard yet (it needs the hitter-side views, wave 2) and no catcher grades of our own. Until then, the Savant boards carry those surfaces, clearly labeled.
Data and provenance
Where every number comes from.
- Sources
- Baseball Savant Statcast (Hawk-Eye; 12-camera era 2023+), MLB Stats API rosters, the Chadwick register for identity (MLBAM ids), FanGraphs Guts for wOBA constants. College and TrackMan data never enter this site.
- Era handling
- The 2026 ABS/plate-tracking convention change is affine re-referenced onto 2023–25 before any model sees a plate column (RESULTS-MLB §10).
- Serving
- The site reads baked JSON from Cloudflare R2 only. It never queries a database or a data mart at runtime.
- Model card
- GOAT-Pro Stuff+ / Pitching+ v2-MLB (csw_norm) — the fingerprint of the exact frozen models behind every grade; also in
meta.jsonin the bucket.
Metrics stripped from the college fork (Loc+, xRV, decision and catcher grades, tunnels, projections) are not defined here because they do not ship yet — see the leaderboard for what does.