What caused A.J.'s breakdown this year?

Unless the Yankees find themselves on the brink of elimination (or eliminated), A.J. Burnett will probably start game four or five of the ALCS. As difficult as it is for Yankee fans to accept, starting the erratic A.J. is the smart move. Given their respective injuries and youth, it is unwise to start either Andy Pettitte or Phil Hughes on short rest. Of the team's remaining pitchers, Burnett is not only the best, but has shown he can step up (or down) in the playoffs. Comfortable with that? Me neither.

The certainty of an always-exciting Burnett start in the ALCS begs the question: What in god's name happened to this guy?

Let's take a look:

All the data are taken from Fangraphs. The left hand table contains data on the percentage of the time Burnett throws various pitches. The right hand table show how effective each of these pitches was in a given season.

True to his reputation, A.J. is primarily a fastball-curveball pitcher, with a changeup that he seldom uses. There is, however, a lot up there that goes against his reputation. The real shocker is how lousy his fastball is. Of the past five seasons, A.J.'s fastball has only been a plus pitch once. Setting aside 2007, it has been anywhere from a bad to an atrocious pitch for him. When you consider that Burnett's fastball has ranged from a low of 93.2 mph on average this season to a high of 95.1 mph in 2007, with considerable horizontal movement, it is shocking to see that this is not a plus pitch for him.

It also sheds light on his problem this season. Surprisingly, Burnett's fastball was just as bad last year as it was this year, except he could protect himself with a positively devastating curve. (For context, CC Sabathia had the most effective changeup in baseball in 2009, with a 23.3 runs above average score, so A.J.'s fastball is among the worst in baseball, and in 2009 his curve was among the best.) This season he couldn't command his curveball. It went from being a weapon, to a slight liability.

Having a pitch that rates slightly below average isn't bad, in and of itself. Earlier this postseason we looked at Andy Pettitte's year and found that his fastball and changeup were below average, but he mixed them in effectively with a plus cutter and curveball. Burnett's only plus pitch is his changeup (shockingly), which he seldom uses. Suddenly A.J.'s struggles are clearer. He's always had a bad fastball in pinstripes, but this season he has no plus pitch that he is comfortable mixing in with it. He can use his fastball (terrible) or his curve (bad), and seldom uses his changeup, even though it is actually his best pitch.

This offers some insight into what to look for from A.J. in the ALCS, and into the later years of his contract with the Yankees (he is totally untradeable). Forget the fastball. Yankee fans have never seen him have a good one. Instead, pay attention to his curve. If he has a tight hook, he may stand a chance in his lone ALCS start because fastball-curveball is a combination he likes.

That is the best thing to hope for on a game-by-game basis this October. In the seasons ahead Burnett certainly needs to get his curve under control, but he also needs to become confident with his changeup. By all measures it is a decent pitch, and could potentially become a weapon if he can learn to mix it in with his other pitchers, especially on nights when he doesn't have his hook working. While that is something to hope for in 2011 and beyond, right now let's hope that Dave Eiland and A.J. are focusing on how Burnett can relearn to throw his curve, at least for one more start.