I was wondering why baseball teams don't use 11 relievers to pitch 2 innings at a time instead of the typical mix of starters, relievers, and closers. Relievers are cheaper than starters and typically have lower ERAs for the innings they pitch. Last night, I heard some compelling reasons why this probably hasn't been tried by Billy Beane.
- Relievers throw fewer innings overall during the season (likely ~60 vs ~200 for starters). If you were to have them throw more innings, they would have higher ERAs.
- Relievers typically throw two or three different types of pitches well, while starters can often throw four or five. This would make hitting easier for batters.
- It would be hard to find enough starters who are transitioning to being relievers to execute this strategy effectively.