Earlier this week, I did an introductory post on relievers and how I use AIPGR and Leverage Index to classify them. In this post, I’m going to look more closely at the members of the bullpen.
Defining relief roles
The closer of a relief staff is fairly easy to identify, since unlike other relievers, closers are judged by saves. So, by setting a baseline for a minimum number of saves, we can determine which pitchers are “closers” (for this post, I’ve set the minimum save number at 20). One-out-guys are also pretty easy to identify using AIPGR. Even though they’re often called that, these pitchers never actually wind up getting one out per appearance on average. Since 2005, only one qualified reliever has actually had an AIP under .5 (Mike Myers had an 0.49 on the 2006 Yankees). I decided I would set an arbitrary line at 0.80. I’ve always assumed that long-guys were used in low-leverage situations in which the only requirement was to eat up innings, and that primarily seems to be the case. Again, I've set an arbitrary AIP cut-off for defining long-relievers. I chose 1.40 as a reasonable number. Finally, we have our middle relievers, which don't fit any of the requirements of the other types of pitchers. I defined "middle relievers" as pitchers with AIP scores between 0.80 and 1.40 that do not meet the save requirement of closers. I split middle relievers into two categories, one with gmLI scores under 1.20, the other with scores at or over 1.20. Here are average numbers for qualified relievers since 2005 in each of the categories.