Bullpen WPA

In the offseason, I think most Twins fans would agree that the bullpen is an area that the front office should be looking to improve. After Pat Neshek’s injury last season, the bullpen became a bit shorthanded, and everyone had to step up and pitch in situations that were a step up from what we had expected at the beginning of the year.

In an effort to grade how our relievers compared to others in the league, I looked at about 40 relievers, chosen by leverage index (i.e., how high-pressure were the situations they pitched in) and number of appearances. Thus I got a few comparison points for the six relievers used most often out of the Twins bullpen, these are all pitchers used in similar situations a similar amount of time.

To examine their effectiveness, I also tallied the number of appearances that resulted in a negative WPA. If they made it any more difficult for their team to win, I counted it as a negative outing. I also looked at “real bad” performances, which I defined as -0.80 WPA or lower. The -0.8 number is somewhat arbitrary, but 0.8 WPA is credited for closing a game pitching an entire inning with a 2-run lead. So I went with the negative of that value for symmetry’s sake.

Here’s the raw data, color coded to keep those used similarly together.


To represent this graphically, everything was converted to percentage of negative WPA appearances.


Also, a plot of the “real bad” performances as percentage of appearances with WPA < -0.8.


Joe Nathan is awesome, Mariano Rivera is the only pitcher close to him in these representations.  Dennys Reyes had a lot of negative WPA appearances, although he was good at avoiding the blow-up outings (probably at least partly due to Gardenhire’s propensity to remove Reyes after a batter or two).  Guerrier and Crain both look pretty bad, while Bass is the middle of the road for relievers with his usage pattern (That usage pattern is pretty easy to replace, so not really the area we need outside help).  Breslow also had a pretty good year as far as preventing big, bad outings.

It is obvious that the loss of Neshek created some strain on the remaining members of the bullpen.  Coming into this year, however, Breslow had perhaps the best year last year of those analyzed here, and with Reyes gone, the Twins will need Breslow or Mijares or Crain/Guerrier to step up and improve the somewhat disappointing performance of last season.

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