How Leaderboard Qualification Works on Baseball Data Hub

A counting stat such as home runs needs no qualification: the player with the most is the leader. A rate stat is different. A batter who goes 3-for-4 in his only game hits .750, and a reliever who throws one scoreless inning has an ERA of 0.00. Every rate-stat leaderboard therefore needs a minimum amount of playing time, and the choice of minimum decides who appears. This guide sets out the minimums Baseball Data Hub uses and why.

Single seasons: 3.1 plate appearances per team game

For batting average, on-base percentage, slugging and OPS in a single season, the site uses Major League Baseball's own rule: a batter qualifies with 3.1 plate appearances per team game. Plate appearances are counted as at-bats plus walks, hit-by-pitches, sacrifice flies and sacrifice hits.

The rule is applied as a rule, not as a fixed number. On a 162-game schedule that is 502 plate appearances, and on the 154-game schedule used before 1961 it is 477, but seasons have not always been either length. The site takes the number of games played by the median club that season and multiplies it by 3.1, dropping any fraction, which is how MLB states its own figures. The 1904 leaders page, for example, is based on a 156-game schedule; the 1981 page on 108 games after the midseason strike; and the 2020 page on the 60-game pandemic schedule, which makes the threshold 186 plate appearances. The median is used rather than any single club's total because a few clubs in the early years played far more or far fewer games than the rest, and the median lands on the schedule the league actually played.

Pitchers qualify for ERA and WHIP with one inning pitched per team game, on the same median schedule. The old flat minimum of 162 innings would have excluded every qualifying season before expansion to 162 games in 1961, and all of 2020.

Every season leaders page prints the rule and the resulting number, such as "3.1 plate appearances per team game — 186 plate appearances at 60 team games", so the arithmetic can be checked on the page.

What the season pages show below the line

A season leaders page lists more players than the qualified ones. Anyone with at least 200 plate appearances or 50 innings appears in the full tables, and players below the qualification line are tagged UNQ and sorted after the qualified players. The category cards at the top show the top ten qualified players only. Counting categories, including home runs, RBI, stolen bases, wins, strikeouts and saves, have no qualification gate at all.

Lahman's data stores one row per team for a player who changed clubs during a season. On the season pages, and on the all-time single-season leaderboards, those rows are combined into one season line, marked "2 teams", so a player traded in July is ranked on his full season rather than on two partial ones.

Career leaderboards

Career rate-stat boards use fixed minimums:

• Career batting average: at least 3,000 at-bats.
• Career ERA: at least 1,000 innings pitched.

Counting-stat career boards, such as career home runs, rank everyone. Each all-time board shows the top 100, with a chart of the top ten. Tied players share a rank, shown with a "T-" prefix, and the next rank skips accordingly, so two players tied for 4th are followed by 6th.

Default boards and combined boards

Every all-time leaderboard comes in two versions. The default board is the traditional record book: the National League, the American League and the four nineteenth-century and early-twentieth-century leagues MLB counts as major (the American Association, Union Association, Players' League and Federal League), with the flat 3,000 at-bat career minimum.

The combined board, linked from each default board, adds the Negro Leagues seasons MLB recognized as major league in 2020. Negro Leagues clubs played schedules of roughly 69 games against the 149 or so that was typical for the AL and NL in the same period, so the combined board prorates the minimums by that ratio:

• A single Negro Leagues season qualifies with 185 plate appearances where the schedule is not known, against 400 for an AL or NL season.
• A career qualifies with 1,389 at-bats when more than half of the player's at-bats came in the Negro Leagues. Players who went on to long AL or NL careers, such as Larry Doby and Monte Irvin, keep the full 3,000.

The proration is what lets Josh Gibson's .466 in 1943 appear on the combined single-season batting average board. The Negro Leagues guide explains where those statistics come from.

PIV boards

PIV (Player Impact Value) is Baseball Data Hub's own measure of a hitter's value against the league average of his season, and Pitcher PIV does the same for pitchers. The single-season PIV boards start in 1901, because the rules of the nineteenth-century game make earlier seasons hard to compare; the career PIV boards include every year. PIV is calculated from completed seasons, so for a season still in progress the PIV pages say which season the figures run through. The formula is on the PIV methodology page.

The current season and the "Data updated" date

While a season is being played, its qualification threshold is based on the games played so far, and the page says so: "at 150 team games played so far", for example. A single-season record set in the current year is tagged in progress, because the figure can still change.

Every page carries a "Data updated" line in the footer. That date is when the underlying statistics were last refreshed from the source, not when the page was last built, so a rebuild on a day with no new games does not move it. During the season the MLB Stats API figures are refreshed daily. Many pages also show their own updated date beside the summary at the top, which changes only when that page's content changes.