On-base average

In baseball statistics, on-base percentage (OBP; sometimes referred to as on-base average/OBA, as the statistic is rarely presented as a true percentage) is a statistic generally measuring how frequently a batter reaches base. Specifically, it records the ratio of the batter's times-on-base (TOB) (the sum of hits, walks, and times hit by pitch) to their number of plate appearances. It first became an official MLB statistic in 1984.

By factoring in only hits, walks and times hit by pitch, OBP does not credit the batter for reaching base due to fielding errors or decisions, as it does not increase when the batter reaches base due to fielding error, fielder's choice, dropped/uncaught third strike, fielder's obstruction, or catcher's interference.

On-base percentage is added to slugging average to determine on-base plus slugging (OPS). The on-base percentage of all batters faced by one pitcher or team is referred to as on-base against.

Traditionally, players with the best on-base percentages bat as leadoff hitter, unless they are power hitters, who traditionally bat slightly lower in the batting order. The league average for on-base percentage in Major League Baseball has varied considerably over time; at its peak in the late 1990s, it was around .340, whereas it was typically .300 during the dead-ball era. On-base percentage can also vary quite considerably from player to player. The record for the highest career OBP by a hitter, based on over 3000 plate appearances, is .482 by Ted Williams. The lowest is by Bill Bergen, who had an OBP of .194.

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