Eno Sarris said not to look at HR rate. He said it and I’m going to listen. However, FIP and xFIP are not HR rates, and I’m going to look at that. Too often we assume that others know, or we actually know, what a statistic represents. We hear it, we think it, we know it. But, take a moment with me to reinvigorate our understanding of these two very important statistics.
FIP gives us an idea of how a pitcher performs regardless of who is playing defense behind him. It accounts for strikeouts, walks, hit by pitches, and home runs allowed. FIP gives us a better understanding of how a pitcher is performing than ERA. xFIP tells us all the same but accounts for the volatility of the HR rate. Quoting from our very own FanGraphs glossary, xFIP is:
calculated in the same way as FIP, except it replaces a pitcher’s home run total with an estimate of how many home runs they should have allowed given the number of fly balls they surrendered while assuming a league average home run to fly ball percentage (between 9 and 10% depending on the year).
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