On-Base Percentage Calculator & Formula
A player's on-base percentage or on-base average, OBP, is an indicator of how often a player reaches base per plate appearance. It does not count events such as a fielding errors, fielder's choice, dropped third strikes, fielder's obstruction, catcher's interference, or sacrifice hits.
Formula for OBPOn-base percentage is not actually a percent but a number between 0 and 1. The equation is
(H + BB + HBP)/(AB + BB + HBP + SF).
It is interesting to compare this number to a player's batting average, BA, given by the simpler formula
BA = H/AB
Rarely a player may have a lower OBP than BA. The mathematical condition for OBP to be less than BA is
(AB - H)(BB + HBP) < (H)(SF)
In other words, a player must have almost no walks or hits by pitch and a relatively high humber of sacrifice flies. This occured in 1982 with pitcher Philip Niekro. He had a total of 87 at-bats, 17 hits, 0 bases on balls, 0 hits by pitch, and 1 sacrifice fly. His OBP and BA were
OBP = (17 + 0 + 0)/(87 + 0 + 0 + 1) = 17/88 = 0.1932
BA = 17/87 = 0.1954
Sabermetricians often add the OBP and SLG (slugging percentage) to create a unified statistic called on-base plus slugging, OPS.
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