Arsenal/Zone Rating: A PitchF/X based pitcher projection system


Abstract: Pitcher performance projection is a fundamental area in baseball analysis. Traditional projection systems are based on either ERA (or RA/9), which cannot separate pitcher performance from fielder defense well; or K%, BB%, HR% and batted ball classification, from which crucial information like BABIP is difficult to derive. These systems leave a lot to be desired. Fortunately, PitchF/X was introduced to baseball, and by utilizing it we can analyze pitchers with much better accuracy. This paper introduces a new and improved method for pitcher projection, which we call “Arsenal/Zone rating”, using PitchF/X data. The idea is that pitcher performance can be mostly judged and predicted from two aspects: arsenal rating, which corresponds to the speed and movement of the pitch, and zone rating, which is related to the location the pitch with regard to the strike zone. Our combined projection stat, when linearly combine our rating with basic pitching stats(K%, BB%, HR%, etc.), is much better than all mainstream projection systems. Our system scores around 25.3% R2 on 2012-2014 qualified starting pitchers when combined with xFIP, while baseline systems (also combined with xFIP) are around 22~23% R2.

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