THE BOOK--Playing The Percentages In Baseball

Monday, October 15, 2007

Replacement Pitchers

Here, with some roll-up sleeves work, are the replacement pitchers of 2007.  Rather than the wrong way of selecting, after the fact, replacement pitchers, magpie figures out, within a certain amount of reason, who the expected rotation was for each team at the start of the season.  And, he gives us the data.  Great work.  The W/L record looks funky, so sticking with ERA (or RA, since I don’t like to remove unearned runs), the league average RA in 2007 was 4.834, and the replacements were 5.795, just about a full run higher than the league average.  This gives us a replacement winning percentage, for starters, of .413.

Don’t forget that the replacement starter also has value as a bullpen guy.  Presuming that these starters would also be in the bullpen, they’d be around .503 as a reliever (.090 win difference between the roles of starter and reliever for the same pitcher).  Giving these pitchers two-thirds of their innings as starters, and one-third as relievers, gives us a pitcher winning percentage of .443.  What does this tell us?  That the guys who do the emergency starts have a winning percentage of .443, if they are used as both starters and relievers.  These guys are obviously better than the 11th pitcher on the team.  I think that this .443 is consistent with calling the replacement-level pitcher as a .410 pitcher, a number I’ve used for a while now.