Stats Glossary

Season-relative qualification

Rate-stat leaderboards need a minimum playing time, or a hot week tops every list. Instead of one flat floor, this site derives the threshold from the schedule each player's teams actually faced: 3.1 plate appearances per team game for batters (the modern MLB rule) and one inning per team game for pitchers. A 154-game 1927 season, a 162-game 1998 season, and a 74-game 1943 Negro National League season each get their own bar.

Career qualification sums the season thresholds a player's teams faced — not a flat 3,000 at-bats. That is why Josh Gibson's documented plate appearances qualify against the 60–80 game schedules he actually played, where a flat floor would erase him. A 100-PA minimum guards against seasons where only a handful of games were documented. Qualified rows are marked with a ✓ in the advanced tables.

OPS vs. League — and why we don't call it OPS+

OPS vs Lg compares a player's on-base and slugging to his league and season: 100 is exactly league average, 150 is exceptional. It uses the same formula as the familiar OPS+ minus the park adjustment, because the Lahman database carries no home/road splits from which park factors could be derived. A hitter in a bandbox and a hitter in a canyon get no correction here — that's a real limitation, and it's why the column is not labeled OPS+.

Two more honest differences from Baseball-Reference's OPS+: our league baseline includes pitchers' batting, so values here read a few points lower than bbref's for the same season; and league context for the Negro Leagues reflects the documented record, which is still being reconstructed.

The advanced columns

PA

Plate appearances: AB + BB + HBP + SF + SH.

ISO

Isolated power — slugging minus batting average; extra bases per at-bat.

BABIP

Batting average on balls in play (home runs and strikeouts excluded).

BB% / K%

Walks and strikeouts as a percentage of plate appearances.

HR/162

Home runs per 162 team games — puts a 74-game Negro Leagues season next to a 154-game one without pretending they're the same length.

K/9, BB/9

Strikeouts and walks per nine innings pitched.

WHIP

Walks plus hits per inning pitched.

Where the numbers stop short

• No park factors. Lahman has no home/road run splits, so every rate here is league-relative, never park-adjusted.
• League baselines include pitchers, so OPS vs Lg runs a few points below Baseball-Reference's OPS+ for the same season.
• Negro Leagues team games reflect documented play. Where the record is thin, schedule-relative thresholds are correspondingly lenient; see The Surviving Record.
• Early-era gaps are honest gaps. Sacrifice flies before 1954 and hit-by-pitch before 1887 weren't recorded, so early OBP is approximate; seasons with unrecorded strikeouts show a dash for BABIP and K% rather than an invented number.
• For the general limits of the data, see the data scope statement.