2009 ERA-xFIP Splits

With 2010 nearly upon us, we’re being inundated with retrospectives recapping all that has occurred over the past year. Let’s add one more list to the mix: starting pitchers with the biggest difference between their Earned Run Average (ERA) and Expected Fielding Independent ERA (xFIP).

Why? Because ERA doesn’t give the most accurate assessment of pitching performance. As Colin Wyers at The Hardball Times showed this past summer, ERA does a rather poor job at predicting future ERA.

Wyers found that xFIP, which is based on a pitcher’s strikeouts, walks and a normalized home run per fly ball rate, has more predictive value than any other pitching metric. In other words, knowing a pitcher’s xFIP tells us more about his skill level and what his future performance may be than simply knowing his ERA would.

A pitcher’s ERA is subject to some factors largely outside of his control. The defensive skill of his teammates plays a part in the rate at which balls put in play are converted into outs. BABIP isn’t entirely out of a pitcher’s control: fly balls have a lower BABIP than ground balls, so fly ball-slanted hurlers tend to have a lower BABIP (the fly balls that aren’t caught are far more damaging, though). Plus, pitchers adept at getting infield pop ups generally have lower BABIP figures, as those are near-automatic outs.

However, team defense can have a large bearing on a pitcher’s ERA. Some get the backing of airtight defenses. The 2009 Seattle Mariners, for instance, saved 12 runs more than the average club per 150 defensive games. Other pitchers get a bunch of plodders and iron gloves. Take the Mets, who were over seven runs below average per 150 defensive games.

Maybe a groundball skips into the outfield for a hit because your second baseman has fall-down range. Or perhaps your world-class center fielder shows off his ridiculous D and runs down a sure fire extra-base hit. ERA doesn’t care either way. Franklin Gutierrez is awesome, but we’re trying to measure the skill of the pitcher here.

A pitcher’s ERA may also be distorted by abnormally high or low home run/fly ball percentages and rates of stranding runners on base. HR/FB rates for pitchers tend to stick around 10-12 percent. Some pitchers may be better than others at throwing from the stretch, but it’s usually a good idea to expect some regression if a guy’s strand rate strays too far from the 70-72% league average.

With all of that being said, here are the starting pitchers (100 inning minimum) with the biggest discrepancies between their ERA and xFIP.

First, the guys who outperformed their peripherals. These are the pitchers whose controllable skills weren’t as good as their ERAs would indicate.

Lower ERA than xFIP

Keep in mind, an appearance on this list does not mean that a pitcher is going to spontaneously combust. You’ll note the presence of Cain, Hanson, Carpenter, Kershaw, Santana, Greinke and King Felix, among other well-regarded starters. It just means that we would expect some regression moving forward. Greinke is a monster (3.15 xFIP), he’s just not likely to go all Pedro Martinez circa 1999 on a regular basis.

Here are the starters whose peripherals were better than their ERAs. These guys performed better than their ERAs suggest.

Higher ERA than xFIP

For some of these starters, you’ll notice strong strikeout-to-walk ratios dragged down by lofty BABIP figures and very low strand rates. Nolasco and Hamels are excellent bounce-back candidates.

When preparing for your 2010 draft, lists like these are a good place to start. But it’s also important to look beyond just the 2009 numbers, taking multiple years of performance into account whenever possible. Due diligence can help you avoid wasting a high draft pick on a ticking time bomb and can help uncover a diamond in the rough.