In baseball statistics, onbase percentage (OBP) measures how frequently a batter reaches base. An official Major League Baseball (MLB) statistic since 1984, it is sometimes referred to as onbase average (OBA),^{[a]} as it is rarely presented as a true percentage.
Generally defined as "how frequently a batter reaches base per plate appearance",^{[1]} OBP is specifically calculated as the ratio of a batter's times on base (the sum of hits, bases on balls, and times hit by pitch) to the sum of at bats, bases on balls, hit by pitch, and sacrifice flies.^{[1]} OBP does not credit the batter for reaching base on fielding errors, fielder's choice, uncaught third strikes, fielder's obstruction, or catcher's interference.
OBP is added to slugging average (SLG) to determine onbase plus slugging (OPS).
The OBP of all batters faced by one pitcher or team is referred to as "onbase against".
Onbase percentage is calculable for professional teams dating back to the first year of National Association of Professional Base Ball Players competition in 1871,^{[2]} because the component values of its formula have been recorded in box scores ever since.
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MLB AllTime Career OnBase % Leaders (18792020)
Transcription
History
The statistic was invented in the late 1940s by Brooklyn Dodgers statistician Allan Roth with thenDodgers general manager Branch Rickey.^{[3]}^{[4]} In 1954, Rickey, who was then the general manager of the Pittsburgh Pirates, was featured in a Life Magazine graphic in which the formula for onbase percentage was shown as the first component of an allencompassing "offense" equation.^{[5]} However, it was not named as onbase percentage, and there is little evidence that Roth's statistic was taken seriously at the time by the baseball community at large.^{[6]}
Onbase percentage became an official MLB statistic in 1984. Its perceived importance jumped after the influential 2003 book Moneyball highlighted Oakland Athletics general manager Billy Beane's focus on the statistic.^{[7]} Many baseball observers, particularly those influenced by the field of sabermetrics, now consider onbase percentage superior to the statistic traditionally used to measure offensive skill, batting average,^{[8]}^{[9]} which accounts for hits but ignores other ways a batter can reach base.^{[10]}
Overview
Traditionally, players with the best onbase percentages bat as leadoff hitter, unless they are power hitters, who traditionally bat slightly lower in the batting order. The league average for onbase 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 deadball era. Onbase percentage can also vary quite considerably from player to player. The highest career OBP of a batter with more than 3,000 plate appearances is .482 by Ted Williams. The lowest is by Bill Bergen, who had an OBP of .194.
Onbase percentage is calculated using this formula:^{[11]}^{[12]}^{[13]}
where
 H = Hits
 BB = Bases on Balls (Walks)
 HBP = Hit By Pitch
 AB = At bat
 SF = Sacrifice fly
In certain unofficial calculations, the denominator is simplified and replaced by Plate Appearance (PA); however, the calculation PAs includes certain infrequent events that will slightly lower the calculated OBP (i.e. catcher's interference, and sacrifice bunts).^{[13]} Sacrifice bunts are excluded from consideration on the basis that they are usually imposed by the manager with the expectation that the batter will not reach base, and thus do not accurately reflect the batter's ability to reach base when attempting to do so. This is in contrast with the sacrifice fly, which is generally unintentional; the batter was trying for a hit.^{[1]}
Alltime leaders
Singleseason leaders
#  Player  OBP^{[15]}  Team  Year 
1  Barry Bonds  .6094  San Francisco Giants  2004 
2  Barry Bonds  .5817  San Francisco Giants  2002 
3  Ted Williams  .5528  Boston Red Sox  1941 
4  John McGraw  .5475  Baltimore Orioles  1899 
5  Babe Ruth  .5445  New York Yankees  1923 
6  Babe Ruth  .5319  New York Yankees  1920 
7  Barry Bonds  .5291  San Francisco Giants  2003 
8  Ted Williams  .5256  Boston Red Sox  1957 
9  Billy Hamilton  .5209  Philadelphia Phillies  1894 
10  Babe Ruth  .5156  New York Yankees  1926 
See also
 List of Major League Baseball career onbase percentage leaders
 Moneyball: The Art of Winning an Unfair Game
Notes
 ^ Not to be confused with opponents' batting average (OBA), more commonly known as batting average against (BAA).
References
 ^ ^{a} ^{b} ^{c} "Glossary / Standard Stats / Onbase Percentage (OBP)". MLB.com. Retrieved 13 June 2018.
 ^ "Yearly League Leaders & Records for OnBase%". BaseballReference.com. Retrieved 20200701.
 ^ "What is a Onbase Percentage (OBP)?  Glossary". Major League Baseball. Retrieved 20200701.
 ^ "Allan Roth – Society for American Baseball Research". Retrieved 20200701.
 ^ Rickey, Branch (August 2, 1954). "Goodby to Some Old Baseball Ideas". Life. Retrieved July 1, 2020.
 ^ Schwarz, Alan (2004). The Numbers Game: Baseball's Lifelong Fascination with Statistics. New York: St. Martin's Press. p. 55. ISBN 9780312322229.
 ^ "Prospectus Idol Entry: Why is On Base Percentage King?". Baseball Prospectus. 20090523. Retrieved 20200701.
 ^ "My plea to mainstream onbase percentage instead of batting average". CBSSports.com. 16 November 2012. Retrieved 20200701.
 ^ "Stat to the Future: Why it's time to stop relying on batting average". www.sportingnews.com. 17 August 2017. Retrieved 20200701.
 ^ "OBP  Sabermetrics Library". Retrieved 20200701.
 ^ "Baseball reference: OBP".
 ^ Cole, Bryan (20140717). "Should the OBP formula include errors?". Beyond the Box Score. Retrieved 20220114.
 ^ ^{a} ^{b} "Fangraphs".
 ^ "Career Leaders for On Base Percentage". Sports Reference, Inc. Retrieved 20110625.
 ^ "Single Season League Leaders for OnBase Percentage". Sports Reference, Inc. Retrieved 20110625.