On base percentage

On Base Percentage (aka OBP, On Base Average, OBA) is a measure of how often a batter reaches base. It is approximately equal to Times on Base/Plate appearances.

The full formula is OBP = (Hits + Walks + Hit by Pitch) ÷ (At Bats + Walks + Hit by Pitch + Sacrifice Flies). Batters are not credited with reaching base on an error or fielder's choice, and they are not charged with an opportunity if they make a sacrifice bunt.

It is possible for a batter to have a lower On base percentage than his batting average, if he has drawn no walks but has hit a sacrifice fly.

All Time Leaders
Span	Player	Total	Notes
Career	Ted Williams	.482
Season	Barry Bonds	.609	2004

There is also an Adjusted statistic called OBP+, which adjusts the OBP to account for the ballpark and the league that the player played in. In addition, the number is "normalized", so that the median is 100, with better-than-average scores above 100. The formula is OBP+ = 100×(OBP÷lgOBP), with lgOBP representing the league average for that year.

Further Reading

• Bill Hagedorn: The On-Base Specialist: A New Model for Baseball Offense, McFarland, Jefferson, NC, 2015. ISBN 978-0-7864-9765-2