ERA-xFIP Splits Update

Last month, we took a gander at starting pitchers who had significant differences between their respective ERAs and xFIPs. xFIP, based on strikeouts, walks and a normalized home run per fly ball rate, does a better job than ERA of gauging performance in the areas over which pitchers have the most control. It’s not subject to more luck-based factors such as batting average on balls in play, strand rate and home runs per fly ball hit.

Now that another month has passed, let’s update the ERA-xFIP lists for the 2010 season. Here are the 20 starters whose ERAs are far lower than their xFIPs (minimum 30 IP for the season):

In general, you’ll note very low BABIPs and home run rates, as well as high rates of stranding runners on base.

As mentioned last time, an appearance on this list does not make a pitcher “bad” or a “fluke” — there are plenty of useful starters here, and at least one elite arm. However, looking at the ERA-xFIP split can make owners view big “breakouts” from the likes of Niemann, Cahill, Buchholz, Pelfrey, Garza and Sanchez with a more skeptical eye. Zito, Fister and Garland are generating more grounders, pitch in front of quality defenders and reside in pitcher’s parks, but those shiny ERAs are going to rise.

And here are the 20 starters whose perhipherals suggest better days are ahead:

This is basically the flip side of the previous list — very high BABIPs and home run rates, and low strand rates. Haren (profiled here), Beckett, Masterson (expect a post on him later this week) and Harang (ditto) stand out here. Jackson isn’t really pitching much differently than he did with Detroit last year, and Peavy isn’t that far off realistic expectations, once you account for his pitching in the DH league in a hitter’s park.