on-base percentage (1941)

“If you substitute the total times a player walks up to the plate and stands there with his bat in his hands for the ‘official at-bats’ and divide it into hits, bases-on-balls, hit-by-pitcher (or the total times a player reaches base) you have an ‘on-base’ percentage that is much more revealing of a player’s value than his ‘batting average’ and ‘slugging percentage’.” Jimmy Powers, “The PowerHouse,New York Daily News, June 3, 1941, p45

No earliest use given in 2009 Dickson Baseball Dictionary