Much Ado About Joba

It was a common topic of discussion this off-season: Should Joba Chamberlain be in the starting rotation or in the bullpen? Much of the mainstream media who had not heard of Chamberlain insisted that he was so good in the bullpen that he must stay there in 2008, while most Yankee bloggers saw confining Chamberlain to the bullpen as a crime. Then came the compromise: begin the season in the bullpen, and move him to the starting rotation around mid-June.

Considering his innings cap in 2008, the compromise would seem to work better than either of the other two plans. If nothing else, it would allow for the rest of the bullpen to sort itself out, allowing other young relief options to become comfortable in the major leagues.

So now the questions presents itself: How effective would Chamberlain have to be in the rotation in 2008 to be as effective as he was in the bullpen last season? I will note that this type of analysis is 100% unoriginal, and I'm stealing it essentially from Nate Silver and from Rany Jazayerli (as he applied it to Joakim Soria yesterday). I am simply applying previously done research and analysis to a different subject. Some of the assumptions I will be using are taken from their work. If you would like to skip the process and go right to the results, scroll past the next two paragraphs.

Let's assume that Chamberlain would throw 85 innings out of the bullpen, if he were to pitch exclusively in that role in 2008, and 140 innings out of the rotation if were to pitch exclusively in that role this season (I won't speculate on how they would limit him, but for now I'll assume that they figured out how to do it effectively). Everyone knows that the 7th, 8th, and 9th innings are more crucial/important than the rest. To account for this discrepancy there is a way to importance of any situation, invented by Tom Tango, called Leverage Index. In simple terms, the higher the number, the greater the importance, or leverage, of the situation. An LI of 1 is exactly average, and the typical middle reliever will have an LI of around 1.5-1.6 (for reference, Okajima was at 1.50, Jon Broxton at 1.47, and Scot Shields at 1.57). Last season Chamberlain had an LI of 1.13, but for this exercise I will assume his LI to be 1.60 since he is not your "typical middle reliever". Keeping Leverage Index in mind, Chamberlain's 85 innings out of the bullpen would equate to 136 innings out of the rotation, which is pretty close to the 140 innings that we assumed he would throw out of the rotation.

That takes care of the relative importance of the innings themselves. Now, onto the performance issue. It is blatantly obvious that almost all pitchers will pitch better in the bullpen than in the starting rotation. For evidence of this, look at recent examples such as John Smoltz, Adam Wainwright, or Brett Myers (for Myers, be sure that you are looking only at his relief stats for 2007). But how much will performance suffer when moving from the bullpen to the rotation? According to Nate Silver, we can expect such a pitcher to "have an ERA about 25% higher when pitching in a starting role than when pitching in relief." Most reasonable people will agree that his 0.38 ERA from last season is unsustainable over a full season, so I'll use his fielding independent ERA (xFIP), as calculated by the Hardball Times, as a measure of his effectiveness (look at it as you would ERA). His FIP last season was a stellar 2.55, rating him as arguably the best set-up men in all of baseball, and one of the best closers, if he had filled that role. If we apply the 25% rule to his FIP, his starters ERA translates to 3.19. This number still seems too low, as he would rank #2 among qualified pitchers. Bumping that number to 3.49 moves him to #9 on the list, a more reasonable number (this still seems too good, but I won't further doctor the numbers to make him look at worse as a starter). (I am fully aware that Rany Jazayerli's Baseball Prospectus column is titled "Doctoring the Numbers," I just thought it was the best phrase to use).

Okay, so that's a lot of numbers being thrown out at you. We assume that Chamberlain would have a 2.55 relief ERA in 80 innings out of the bullpen, and calculate that that would be roughly equivalent to a 3.49 ERA in 140 innings as a starter, even taking leverage into account.

Now that we have data and projection to work with, we can see the relative performance necessary in each role to determine which is more valuable to the team. If my vote counts, I say bullpen for ten weeks, 2-3 weeks in the minors and/or long-relief building up arm strength, followed by a move to the rotation.