The Tune Was An Old Rebel One: Has Matt Cain Broken xFIP?

Matt Cain has come up a bit recently as a player who has supposedly "broken" xFIP (expected Fielding Independent Pitching) by being able to keep an inordinate number of flyballs in the park. Now, for those who don't know, xFIP is essentially a version of FIP (a statistic that estimates luck- and park-neutral ERA based on K-, BB-, and HR-rates on a per-inning basis) that normalizes HR/flyball-rates to league-average based on the underlying assumption that pitchers can't really control whether or not flyballs become homeruns.

So, first and foremost, it's important to keep in mind that Matt Cain is a post hoc example, which essentially means that we're picking him out after he's done it. If you look at enough players someone is going to deviate from the norm, simply by random chance. However, Cain isn't entirely post hoc, people have been talking about this possibly being a skill for him for quite some time now. For that reason, we'll ignore the post hoc aspect of this for now and look at how Cain has kept flyballs in the park.

Well, first, it should be noted that Cain makes roughly half of his starts at home -- AT&T park in San Francisco is notable as a stadium that greatly reduces the likelihood of flyballs becoming homeruns (its MLB ranks for HR park factor between 2007 and 2012: 24, 13, 20, 20, 30, 30). So, the fact that he's playing a pitcher-friendly park already makes flyballs less likely to become homeruns. However, even more interesting, is which homeruns AT&T actually suppresses. Homeruns to leftfield (generally hit by righthanded batters) are not actually being suppressed much at all but homeruns to right are suppressed to the extreme.

Naturally, this means that it's going to be much more difficult for lefthanded batters to hit homeruns at AT&T than righthanded batters. Since 2007, just 7.7% of flyballs hit by lefthanded batters have left AT&T park. By contrast, righthanded HR/fly-rate is 8.4%. The same HR/fly trends emerge when we look at Cain's own career splits (vs. righties: 6.8%, vs. lefties: 6.3%).

Now, this is actually quite important because teams stack their lineups against Cain with lefties. Roughly half of all batters Cain has faced are lefties (50.0%). Compare that with San Francisco's staff as a whole in 2011 (just 37%) and it makes sense that the park actually helps Cain even more than park factors, which estimate how much it helps the staff as an whole, would indicate.

That's not all, however. Cain's division rivals are not exactly known for their bats. Take a gander at the quality of the offence in Cain's division since 2007:

Team	HR/fly (%)	wRC+
Padres	8.5	92
Dodgers	8.6	94
Diamondbacks	10.3	90
Rockies	10.9	95

Two of Cain's road parks are hitter's parks (Arizona and Colorado) but the effects of those hitter's parks are largely offset by there being two pitcher's parks (San Diego and Los Angeles). More importantly, the quality of the offences in Cain's division are all quite a bit below average -- in spite of the fact that they play half their games in hitter-friendly parks, their HR/fly-rates are still no better than league average. Compare this to the AL East over the same time period, for example:

Team	HR/fly (%)	wRC+
Yankees	12.9	114
Red Sox	10.7	111
Rays	11.0	106
Orioles	9.6	95
Blue Jays	10.5	99

The Orioles, easily the worst offensive team in the AL East over the past five years have been as good (in a park-neutral context) as the best offensive team in the NL West. The Jays, an average offensive team for the league and well below-average for the division over this period, would have been the best offensive team in the NL West by a considerable margin. What this means is that, even though he has to pitch in Arizona and Colorado, their offences are weak enough that they're essentially league average offences, even at home. And when they come to San Francisco, they're going to be far worse. Suffice it to say that Cain is facing inferior competition.

Thus, I think Cain's "true" HR/fly-rate is likely quite a bit higher than what we've seen. On the road, Cain's career HR/fly-rate is 7.0%. Given that his park suppresses lefthanded batters as much as any park in the game and, on top of that, he's facing some of the weakest offences MLB has to offer, it seems like his HR/fly-rate should be a quite a bit higher than that, even.

Now, all this is not to say that Matt Cain is not a very good pitcher. In fact, it doesn't even mean that Cain does not possess some skill to keep flyballs in the park; on the contrary, Cain is absolutely a very good pitcher and, even accounting for these factors, it seems like he has been somewhat more successful than a league average pitcher would have been. So it is true that xFIP may consistently underrate Cain's true abilities, but, considering that his "true" HR/fly-rate should more likely be somewhere in the 7-8% range, it seems like he's hardly "broken" it. Especially considering he's a post hoc example. Either way, Brian Sabean was once interested in trading Cain for a young outfielder with decent power potential but no plate discipline . . . any chance you think he might take a flier on Eric Thames?

Today's post title comes from a The Clash's great "Rebel Waltz"