THE BOOK--Playing The Percentages In Baseball

Thursday, April 02, 2009

Should your bullpen carry lefties?

Here is an article by Geoff Baker in the Seattle Times about the fact that the M’s will open the season without a lefty in the pen. Keep in mind that our own Tangotiger (or is it Tangotigre? ) consults for that newest (and woefully in need) sabermetric team.

http://blog.seattletimes.nwsource.com/mariners/2009/04/02/no_lefties_in_pen_done_before.html

Anyway, it is kind of a silly argument. Or I should say the way you will generally see it argued is silly.  One of MGL’s “rules” is that a controversial subject is only as “good” as the quality of the debate surrounding it.

Anyway, one really silly way to debate something like that is by showing us teams that have or have not been successful with no lefties in the pen.  The reason, it is a really silly part of the discussion is that the nexus between a team’s win/loss record and how many lefties they have in the pen regardless of how valuable those lefties are or are not is incredibly remote.  IOW, looking at team success historically with or without lefties in the pen ain’t going to shed any light on the issue.  None whatsoever (well, not exactly zero, but pretty close to it).

Anyway, there is nothing magical about having lefties in the pen other than the fact they tend to be better at getting lefty batters out (same for RHP and RHB, although not to the same degree).  The price you pay is having to use up more roster spots.  Obviously a good RHP with a small platoon split is about the same versus lefties as a mediocre lefty.  So the question is not whether to have a lefty or lefties in the pen or not - it is how good is your bullpen versus lefty and righty batters overall and how many spots does it take to get where you want to be.  If you have very good RHP with small platoon splits, you probably don’t “need” lefty relievers. If you don’t, you probably do. If you have lefty relievers who are good and have low platoon ratios themselves, then you don’t need as many RHRP.  So it really has nothing to do with having lefties in the pen or not.  It has everything to do with how your bullpen overall will do versus RHB and LHB.  If you can, you want to make sure that you can handle both AND that you have the flexibility of being able to do that 2 or 3 times a game, since you have to take out relief pitchers all the time during a game, especially in the NL.  That can be handled with 2 or 3 lefties in the pen. (In fact, for that reason, it is better to have good relief pitchers with low platoon splits, so that you don’t have to keep taking them in and out of the game.) That can be handled with 1 lefty in the pen.  Or given the right kind of RHRP, that can be handled with no lefties in the pen. This “debate” is like having a debate over whether you should have good pitching, good fielding, or good hitting on your team. Obviously you want to have the best combination of all 3, given the resources you have…