Red Sox: How Steven Wright got his groove back

Due for a Regression

The prolific results produced by Wright in his first 14 starts were unlikely to be sustainable as indicated by the discrepancy between his FIP and ERA during that period.

FIP and ERA are typically in remarkable agreement, and when they are not, specifically when one’s FIP is much larger than one’s ERA, it indicates that said pitcher has been the beneficiary of short-term fluctuations in luck. The premise behind FIP is to eradicate these short-term fluctuations in luck, both positive and negative, and, as a result, provide a much better indicator, and predictor of performance than ERA.

Specifically, FIP eradicates the short-term fluctuations in BABIP, or Batting Average of Balls in Play, by assuming a league-average value for said statistic, as these fluctuations have nothing to do with “skill,” but are primarily the result of “luck.” The league average for BABIP is around .297, and given a substantial enough sample size, practically all pitchers will be within a few points of this value; however, for short periods, luck can render this value significantly higher or lower. When the FIP is larger than the ERA, the pitcher has been the beneficiary of good luck, and when the FIP is smaller than the ERA, it indicates that the pitcher has been the victim of bad luck.

In his first 14 starts of 2016, Wright’s ERA was 2.01 and his FIP was 3.30. During said period, Wright’s BABIP was .247, well below the league average of .297. What this indicates is that Wright had been the short-term beneficiary of an unsustainable BABIP, and when his BABIP eventually regressed toward the mean, his ERA value would approach his FIP value.

Wright’s ERA was due to regress towards his FIP, and said regression culminated in his 15^th start of 2016.

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