Sunday, May 4, 2008

Middle reliever ERA

I highly recommend that people not post ERA (or ERA+ for that matter) to say how good/bad a middle reliever is. It can be very misleading because of inherited runners. If a middle reliever enters a game with men on base, the question of whether or not he prevents the baserunners from scoring doesn't affect his ERA. Also, if the middle reliever leaves a game with runners on base, his ERA is affected by how well the reliever after him pitches, which is out of the control of the middle reliever in question.

I'll give you a couple of points to keep in mind before I explain what I do to counter the issue of a middle reliever's ERA. 1) There's no consensus of what stats should be used for a middle reliever. Different stats have different strengths and weaknesses. 2) I'm no sabermetrician by any means. Fortunately that means the feedback I'll give will be easy to understand and easy to find for a player. I'll also mention stats that are recommended by URISoxFan, who knows way more about stats than I do. If you want to do your own sabermetric research, there are plenty of stats and explanations in the SoSH wiki's Statistical Reference Page.

The two sets of stats I use most often for a middle reliever are:
1) Opponents' AVG/OBP/SLG. Espn.com gives additional breakdowns for this stat like Vs. LHP, Vs. RHP, or by situation: what runners are on what bases and with how many outs. Keep in mind that the more you break these down, the greater the chance you're dealing with SSS (small sample size) because a middle reliever pitches in different situations only so many times per season. Unlike ERA, opponents' AVG/OBP/SLG isn't affected by how well the reliever after the reliever in question pitches.
2) IP, H, BB, K. A weakness is that it doesn't factor singles vs. extra base hits like opponents' SLG does. However, this set of stats gives more specific data than middle relievers' ERA, and it isn't affected by how well the reliever after the reliever in question pitches. It's also more specific than WHIP because it separates hits from walks.

URISoxFan gave me feedback of a middle reliever's stats that he recommends for people who want to use stats that are easy to find and easily understood. They are:
K/9
BB/9
HR/9
Innings/appearance (for usage)
K/BB (for command)

For the very few who might not know, "/9"="per 9 innings pitched".

FWIW, URISoxFan tends not to like using hitters' rates because of their dependence on defense/ballpark/quality of opponent. As I said, different stats have different strengths and weaknesses.

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