Zack Greinke In ‘The Peripheral Disconnect’
Pitchers whose ERAs and estimators disagree are extremely interesting to analyze. On one hand, their signature run prevention mark might appear toward the top of leaderboards while the underlying numbers aren’t as fruitful. On the other side of the spectrum are pitchers like Zack Greinke, who, as Chris Cwik pointed out yesterday, has a vast disconnect between his ERA and FIP. In fact, it’s been that way since the first week of May when he came off of the disabled list.
His 2.63 FIP and 2.12 xFIP suggest that the newly-minted Brewers starter has been one of the best in the league. But Greinke’s actual 5.63 ERA is closer to the bottom than the top, and is three runs higher than his adjusted marks. One of the more popular stats here is E-F, a sortable number that measures the gap between ERA and FIP. Pitchers with a large separation are expected to regress in some fashion, because it is incredibly rare for anyone to finish with a huge disagreement between those two data points.
I thought about taking that concept a bit further and calculating the difference between ERA and xFIP, since the latter metric is a better predictor of future earned run average than its predecessor. This makeshift ‘E-X’ number would be measurable from 2002-now, and it piqued my curiosity to see which pitchers had the largest such gaps in that span.

