This is where we explain new or changed features on the site in plain language. We'll add a new entry here each time something changes.

Park factor methodology varies slightly from site to site, so this figure (and stats that use it, like wRC+) may differ a bit from what you see elsewhere.

Batter Stats

wOBA	Combines AVG/OBP/SLG into one number, weighting each outcome (walk, single, double, home run, etc.) by how much it actually contributes to scoring. Roughly .320 is league average, .350+ is good, .370+ is elite, below .290 is below average.
wRC+	Park- and league-adjusted measure of a hitter's run-producing value versus league average (100). 120 means 20% more run production than average.

Pitcher Stats

BABIP	Probability that a ball in play becomes a hit. Values far from the average tend to regress toward the mean. Roughly .290-.300 is average.
FIP	An ERA-like metric based only on what a pitcher directly controls (strikeouts, walks, home runs), independent of defense or luck. With enough sample size, it predicts the next game better than ERA. On the same scale as ERA: 3.50 or below is excellent, around 4.00 is average, above 4.50 is below average.
xFIP	FIP with home runs replaced by the league-average HR/fly-ball rate, removing home-run luck (park/season variance) as well. With a large enough sample it predicts future results even better than FIP. Same scale as FIP: 3.50 or below is excellent, above 4.50 is below average.
K-BB%	Strikeout rate minus walk rate - a key measure of how favorably a pitcher works the count. Roughly 10% is average, 15%+ is good, 20%+ is elite.
LOB%	Share of baserunners a pitcher strands without allowing them to score. Extreme values tend to regress toward the mean, so it's used to gauge how much luck was involved. Roughly 72-73% is average.
WHIP	Walks plus hits allowed per inning pitched. Lower means fewer baserunners allowed. Roughly 1.30 is average, 1.20 or below is good, below 1.00 is elite, above 1.40 is below average.

Team & Stadium Stats

Pythagorean Win%	Win percentage estimated from runs scored/allowed. A large gap from the actual win rate suggests the team's record is over/underrated by luck.
Park Factor	Park Factor = (Avg. runs at home / Avg. runs on road) x 100

To show splits by opposing-batter handedness and other situational stats, we collect and aggregate raw pitch-by-pitch data ourselves - going beyond what any official API provides. Because game situations vary so much, some edge cases are unavoidable even so. We keep improving accuracy, but the items below currently have known gaps or aren't supported at all, due to limits in our data source or how we calculate them.

AI (Anthropic Claude) is involved in this site's data validation and analysis work - the error rates listed below are figures Claude verified directly against our database.

NPB

vs L/R ERA

NPB doesn't support a vs-LHB/vs-RHB ERA at all (shown as "-" on screen) - our NPB data source (Yahoo Japan) has no run-scoring information whatsoever, so it can't be calculated.

MLB

vs L/R ERA

MLB doesn't provide a vs-LHB/vs-RHB ERA either (shown as "-" on screen). Which pitcher is responsible for a run (inherited runners included) is accurate, straight from MLB's own official ruling - but unlike hits or walks, a run isn't cleanly tied to one plate appearance (a runner often reaches base, then scores several batters later off someone else's at-bat). In fact, 74.3% of runs this season were scored on a different batter's plate appearance than the one that put the runner on base. With no reliable way to say which handedness bucket a run belongs in (most other sites don't attempt this stat either), we chose not to show an error-prone number rather than provide one. The rest of the plate-appearance-based stats - FIP, WHIP, BABIP, K-BB%, AVG/OBP against, wOBAA, etc. - are unaffected by this and remain accurate.

General

Right after a season opens, some games may not have finished detailed processing yet, so a few advanced stats can be based on an even smaller sample than the figures noted above.

Park Factor

Park factor methodology varies slightly from site to site, so this figure (and stats that use it, like wRC+) may differ a bit from what you see elsewhere.