Of course, if one is a fan of the Washington Nationals, this can create some upsetting reading. When I first stumbled over baseball on 'teh Intertube', as they say at Baseball Primer, DIPS had just hit version 2.0, I think, or was about to. The theory of DIPS is that pitchers have very little influence on the outcomes of balls in play. Out of the DIPS debate emerged FIP, or Fielding Independent Pitching, a way of calculating an ERA that set to one side the balls in play. And then the chaps at Hardball Times developed xFIP, which adjusts the home runs allowed in relation to the ratio of fly balls allowed by the pitcher. (Their research seems to indicate that a pretty consistent percentage of fly balls go for home runs, once one adjusts for the effects of the ballpark, and random variations.)
The objective of xFIP is to find a number that will more accurately predict a pitcher's future ERA. It works a bit better for starters than for relievers, although you can use it with caution for relievers. So, how about those Nationals?
Remember, these numbers don't include fielders booting balls, or just not having the range to get to a grounder. This is strikeouts, walks and home runs. It's pretty horrific, especially a closer with a 3.90 xFIP — relievers, to be useful, generally need to be at least half a run better than an average starter, and closers more like a run or more.
Basically, going by xFIP, Zimmermann looks good going forward, Detwiler is about a league average pitcher, and Lannan and maybe Stammen can fill out the back of a competitive team's rotation. And, as of 5 June 2009, that's all Nationals' fans have in the whole bullpen that's really worth keeping.