Thursday, February 24, 2011

A Statistic that WERCs for Relievers

I'm not really sure how good Weighted Component ERA (WERC) is for evaluating relievers, but it's a good statistic for silly blog titles.  I originally Introduced WERC in an earlier post and applied it to MLB starters in 2010.  To review, it serves as an intermediate step between ERA and FIP.  The FIP statistic estimates what a pitcher's ERA should have been based on fielding independent statistics - walks, hit batsmen, strikeouts and home runs.  WERC is another ERA estimator, but it adds hits to everything that FIP includes.

Why might WERC be useful for relief pitchers?  There is growing evidence that relievers (especially very good ones) have more control over the results of batted balls than starters.  The phenomenon has been studied by Lewie Pollis of Wahoo Blues and Dave Studenmund at The Hardball Times among others.  It has been found that at least some relievers tend to allow fewer hits on batted balls throughout their careers than most starters.

One theory is that relievers only have to pitch to a few batters per game and can throw their best stuff on every pitch, whereas starters need to pace themselves throughout the game.  Therefore, relievers may be able to induce weaker contact than starters.  With this in mind, it might make sense to include hits in the evaluation of relievers even if it has been shown that most starters have limited control over batted balls.  Thus, WERC might be a good alternative to FIP in evaluating relievers. 

The top relievers (according to WERC) with 50 or more appearances in 2010 are listed in the table below.  Dodgers left-hander Hong-Chih Kuo led the majors with a fantastic 0.84 WERC.  He also finished first in ERA (1.20) and second in FIP (1.81).  His extremely low WERC along with his .206 Batting Average on Balls in Play (BABIP) both show that he was very good at limiting hits.  It's not likely that he can maintain the same WERC or BABIP next year, but relievers do tend to have lower BABIPs than starters.

New Tigers reliever Joaquin Benoit finished third in the majors with a 1.15 WERC pitching for the Rays last year.  We'll look at more Tigers relievers in a later post.  

Table 1: Top 20 Relievers by WERC in 2010

Note: Some of the data for this article were taken from Baseball -Reference and FanGraphs

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