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On-base percentage

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 measure of how often a batter reaches base for any reason other than a fielding error, fielder's choice, dropped/uncaught third strike, fielder's obstruction, or catcher's interference (the latter two are ignored as either times-on-base (TOB) or plate appearances in calculating OBP). OBP is added to slugging average to determine on-base plus slugging (OPS). It first became an official MLB statistic in 1984.

Overview

Traditionally, the best leadoff hitters in the game have high on-base percentages. The league average for on-base percentage has varied considerably over time; in the modern era it is around .340, whereas it was typically only .300 in 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.

Though extremely unlikely, it is possible for a player's on-base percentage to be lower than his batting average (H/AB). However very few players in major league history fall into this category, with the majority of them having under 100 ABs, as it requires having almost no walks or times hit by pitch, with a relatively higher number of sacrifice flies (e.g. if a player has 2 hits in 6 at bats with a sacrifice fly, his batting average would be .333, but his on-base percentage would be .286). An example of this phenomenon would be the Hall-of-Fame pitcher Phil Niekro's hitting statistics from 1982. In 87 AB he never walked, but had four sacrifice hits, leading to a Batting Average of .195 and an OBP of .193.

On-base percentage is calculated using this formula:

OBP = frac{H+BB+HBP}{AB+BB+HBP+SF}

where

NOTE: Sacrifice flies were not counted as an official statistic until 1954. Before that time, all sacrifices were counted as sacrifice hits (SH), which included both sacrifice flies and bunts. Bunts (sacrifice hits since 1954), which would lower a batter's on-base percentage, are not included in the calculation for on-base percentage, as bunting is an offensive strategy – often dictated by the manager – the use of which does not necessarily reflect on the batter's ability and should not be used to penalize him. For calculations of OBP before 1954, or where sacrifice flies are not explicitly listed, the number of sacrifice flies should be assumed to be zero.

All-time leaders

#	Player	OBP	Team(s)	Year(s)
1	Ted Williams	.4817	Boston Red Sox	1939–1960
2	Babe Ruth	.4740	Boston Red Sox, New York Yankees, Boston Braves	1914–1935
3	John McGraw	.4657	Baltimore Orioles, St. Louis Cardinals, New York Giants	1891–1906
4	Billy Hamilton	.4552	Kansas City Cowboys, Philadelphia Phillies, Boston Beaneaters	1888–1901
5	Lou Gehrig	.4474	New York Yankees	1923–1939
6	Barry Bonds	.4443	Pittsburgh Pirates, San Francisco Giants	1986–2007
7	Bill Joyce	.4349	Brooklyn Ward's Wonders, Boston Reds, Brooklyn Grooms, Washington Senators, New York Giants	1890–1898
8	Rogers Hornsby	.4337	St. Louis Cardinals, New York Giants, Boston Braves, Chicago Cubs, St. Louis Browns	1915–1937
9	Ty Cobb	.4330	Detroit Tigers, Philadelphia Athletics	1905–1928
10	Todd Helton	.4284	Colorado Rockies	1997–September 28, 2008
11	Jimmie Foxx	.4283	Philadelphia Athletics, Boston Red Sox, Chicago Cubs, Philadelphia Phillies	1905–1942, 1905–1942
12	Tris Speaker	.4280	Boston Red Sox, Cleveland Indians, Washington Senators, Philadelphia Athletics	1907–1928
13	Albert Pujols	.4250	St. Louis Cardinals	2001-September 28, 2008
14	Eddie Collins	.4244	Philadelphia Athletics, Chicago White Sox, Philadelphia Athletics	1906–1930
15	Ferris Fain	.4241	Philadelphia Athletics, Chicago White Sox, Detroit Tigers, Cleveland Indians	1947–1955

bold is active player

Single Season Leaders

#	Player	OBP	Team	Year(s)
1	Barry Bonds	.609	San Francisco Giants	2004
2	Barry Bonds	.582	San Francisco Giants	2002
3	Ted Williams	.551	Boston Red Sox	1941
4	Babe Ruth	.542	New York Yankees	1923
5	Barry Bonds	.529	San Francisco Giants	2003
6	Babe Ruth	.528	New York Yankees	1920
7	Ted Williams	.526	Boston Red Sox	1957
8	Billy Hamilton	.517	Philadelphia Phillies	1894
9	Barry Bonds	.515	San Francisco Giants	2001
10	Ted Williams	.512	Boston Red Sox	1954