THE BOOK--Playing The Percentages In Baseball

Tuesday, June 19, 2007

The Replacement Pitchers

Sean chimes in:

How good (or bad) is a replacement level starting pitcher?  I tried to answer this by looking at all starting pitchers for 2007, and ... take out all pitchers who started the season in the rotation, those who would have started had they not been injured, top prospects (those who made Baseball America’s top 100 list), and Roger Clemens.

THAT is about as perfect a definition of replacement-level starter as there is.  Note, this is NOT the same as a replacement-level pitcher in a starterRole.  After all, where do you find a replacement-level starters?  In the bullpen!  And those guys are (slightly) better than the scrap heap.

How are they doing for 2007?  After taking out the non-replacements, as well as any pitcher who made more than half of his appearances in relief, I have 952 innings with a 5.03 ERA, against a league average of 4.32.  That’s a winning percentage of .430

I don’t get the “relief” condition.  Personally, we should stick with only performance in starterRoles.  Fangraphs and Baseball-Reference both give you the necessary breakdown.  In any case, as I’ve shown in the past, here’s our benchmarks:
- replacement-level pitcher in a starterRole: .380
- replacement-level pitcher in a relieverRole: .470
- average starter in a starterRole: .490
- average reliever in a relieverRole: .520

As you can see, the relief-to-start adjustment is about -.090 wins.  So, an average reliever in a relieverRole (.520) would translate to .090 less than that in a starterRole, or.... .430. 

Ace relievers are not candidates for a starterRole, and if we assume that they make up 1/6th of the relief pool, and, in a relieverRole, they are .600 pitchers, then the .520 breaks down as: .600 for ace relievers, .500 for average reliever, all in a relieverRole.  That .500, subtracted by .090, gives us .410 for non-ace relievers in a starterRole.  Therefore, my best guess as to what a replacement-level starter looks like (guys in the bullpen who are not ace relievers) is a .410 pitcher in a starterRole.

Because Sean’s pool of pitchers is overweighted by Guthrie, I’d bet he’d get numbers around .410.