Mains: Running relievers ragged

From SABR member Rob Mains at Baseball Prospectus on June 29, 2017:

Last week, I introduced—OK, made up—the LIP Index as a way to measure wear and tear on relief pitchers. The LIP Index is simply the product of innings pitched and the average Leverage Index during a reliever’s appearances. It measures both the volume of a reliever’s work (innings) and the pressure he faces during his games (leverage). The LIP Index leaders last year were Sam Dyson, David Robertson, Steve Cishek, and Dellin Betances.

I also checked whether accumulating a high LIP Index portends future problems. Are hard-worked relievers more likely to break down? To find out, I looked at the 15 pitchers who compiled the highest LIP Index through the All-Star break last year. To my surprise, they posted a lower average ERA and a higher strikeout rate after the break. Only three of the 15 were unquestionably worse after the break. So in the case of relievers, at least, it appears that high-leverage workloads in the first half of the season don’t foretell problems later on.

Or maybe they do. I looked at pitchers within a season. As my editor, Aaron Gleeman, asked me, what happens year-over-year? Does a pitcher who sustains a heavy LIP Index workload in a season have problems the following year?

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Originally published: June 29, 2017. Last Updated: June 29, 2017.