of the game. On some occasions, teams would use multiple relievers who could pitch only one or two innings after the opener; this became known as a bullpen game. Due to their lighter workload and conditioning, openers are able to pitch more frequently than a traditional starter.

In the early decades of baseball, it was not uncommon for a starting pitcher to pitch 300 innings or more, over the course of a season. In addition, there are accounts of starting pitchers pitching on consecutive days, or even in both games of a doubleheader.