Bullpen by Committee (1983)

“The Orioles have Tippy Martinez in the bullpen, but the White Sox have a bullpen by committee that is no less impressive.” Greg Boeck, Democrat and Chronicle (Rochester, NY), October 2, 1983, p1E

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
The term was used by manager Whitey Herzog for the 1985 St. Louis Cardinals bullpen staff in which he used everybody, but it is now applied widely to relief staffs from which different pitchers are used depending on the game situation.