Closer to Optimal: Trends in Bullpen Usage

by Mike Emeigh


Perhaps no aspect of modern baseball has received as much criticism as the reservation of one pitcher – the closer – for ninth-inning save situations. In the recent The Book: Playing the Percentages in Baseball, the authors introduce the concept of leverage – a measure of the game importance of a given situation – and argue for the use of the best reliever in high-leverage situations that occur earlier than the ninth inning. Almost every study of bullpen usage focuses on optimizing the role of the closer. But the closer is only one member of the bullpen, and changing the closer’s usage would inevitably have a ripple effect on the rest of the relievers. Without understanding how the closer’s role fits into the context of a modern bullpen, and the factors that affect how teams use all of their relievers, it is difficult to assess the impact that a change to the closer’s role would have on the team. This presentation provides an assessment of recent trends in reliever usage. Using Retrosheet data and the leverage concept developed in The Book, we can identify when relievers are brought into games and define the roles that they typically fill on their teams. This in turn should allow us to build a model for bullpen usage, and for evaluating the effect of role changes in the bullpen.


Mike Emeigh is a contributing writer for Baseball Think Factory ( and edits BTF's Minor League blog. In 2002, he wrote an eight-part series on fielding metrics for BTF, and is currently writing a series of articles tracing the evolution of pitcher usage, from which the poster presentation presented at this conference developed. He is a 1977 graduate of Carnegie-Mellon University and is employed as a Software Quality Assurance manager for a major telecommunications company in Raleigh, NC.

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