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The best single seasons ever, grouped by how old the player was: 21-and-under, 25-and-under, 35-and-over and 40-and-over, batting and pitching, 1871-2025. Every board is era-normalized (league-season OPS+ and ERA+) so a 19th-century season and a modern one can be compared honestly.
A season's age is the player's age as of June 30 of that season year, the same convention Baseball-Reference uses. A player born in January through June is a full calendar year older than a teammate born in July through December of the same year. A July 1 birth, for example, means the whole-season age is one less than the calendar-year difference: born July 1, 2000, the player is 20, not 21, for the entire 2021 season.
Batting boards rank league-season-normalized OPS+ (100 x OBP/lgOBP + SLG/lgSLG - 1); pitching boards rank league-season-normalized ERA+ (100 x league ERA / pitcher ERA). Neither is park-adjusted, and neither is the full Baseball-Reference formula. Qualifiers follow the era-consistent rule used across the historical boards: batters need 3.1 plate appearances per scheduled team game, starters an inning per scheduled game, relievers a third of that. Every row with a committed career page links to it; players outside our top-3,500 career-page set render as plain names.
The records come from the SABR / Sean Lahman baseball database (2025 edition), used under Creative Commons Attribution-ShareAlike 3.0. See the sources page for every dataset behind Legends Deck.