Last year at the All-Star break I did a piece that collected all the pitchers who had a difference of at least 0.50 between their FIP and xFIP. At the end of the season I collected the 2nd half ERA for each pitcher in the survey to see if FIP or xFIP did a better job of predicting the results. The raw results favored xFIP, as that metric did a better job predicting 20 of the 34 pitchers. However, FIP did a better job of predicting how the best pitchers in the group would fare.
The results were definitely interesting, but it was hard to make any proclamations off one year of data. So, now is the time to assemble this year’s chart of pitchers with a discrepancy of at least half a run between their FIP and xFIP. Like last year, this list was crafted by hand, so please let me know if you see any omissions. I am looking for pitchers who had 70 or more innings pitched at the All-Star break.
This year there are 38 pitchers in our survey. Five pitchers are repeats from a season ago – Kershaw, Lee, Blackburn, Verlander and Bannister. However both Blackburn and Bannister had HR/FB rates below average last year at the break while they are both above average this year. Kershaw, Lee and Verlander are the only ones who “beat” the average HR/FB rates in both seasons. As far as predicting 2nd half ERA goes, Kershaw and Lee were wins for FIP while xFIP did a better job of predicting Verlander.
To determine which metric is better at forecasting 2nd half ERA, I am going to take the midpoint between their FIP and xFIP and compare it to their real life ERA in the second half of the season.
Using Kennedy as an example, 4.57 is the midpoint between his FIP and xFIP. So, if Kennedy’s ERA in the second half is 4.44, I will count that as a “win” for xFIP. On the flip side, if Kennedy’s second half ERA is 4.66, I will count that as a “win” for FIP.
Like last year, I will check in on this list after the end of the regular season.