Where Have A.J. Burnett’s Strikeouts Gone?

Following Wednesday night’s disastrous start (3.1 innings pitched, two homers, and more walks than strikeouts) A.J. Burnett has now faced 382 batters on the season. Two hundred batters faced is the amount Pizza Cutter established as the threshold for strikeouts/plate appearances to become a reliable metric during a single season. That’s worth noting because Burnett’s strikeout percentage sits at 16.5%. Over the last three seasons, he struck out 23.7% of batters faced; over the last five that number is 23%; for his career it’s 21.7%. As it stands, the only season in which Burnett struck out batters at a lower rate than he is currently was way back in 2000. That year, he struck out 15.7% as a 23-year-old

When Burnett signed with the Yankees, the expectation was that his numbers could actually improve. He was battle tested in the rough American League East. More important than battled tested, though, he was successful. His xFIP had ranged from 3.55 to 3.64 over his three-year stint with the Jays, and a move to the Yankees meant he would no longer have to face a lineup consisting of multiple Hall of Famers on numerous occasions each season. That hasn’t been the case, though.

It was probably unrealistic to expect Burnett to improve on his whiff rate, which was over 10% in 2008, but that figure declined to 8.2% in 2009, and sits at 7.1% in 2010. A once raging fastball, sitting in the upper 90s on some occasions, has retreated in velocity. Pitchfx has its average velocity sitting just about 93 miles per hour, with empty swings occurring under 6% of the time. The only pitch Burnett is actually having batters miss often is his knuckle curve (12.5%). Compare that to last season and the only noticeable changes have nothing at all to do with his velocity being down. He’s actually getting more whiffs on the fastball and fewer on the curve.

That would suggest the decline is not entirely due to his velocity, which leaves predictability and location as the other potential culprits. The curve becomes Burnett’s go-to pitch when he reaches two strikes. With the exception of 3-2 counts, Burnett tosses his bender more than 50% of the time on each count. This doesn’t differ too much from 2009, when he threw it 60+% of the time on 0-2 and 1-2 and 48% on 2-2. This usage pattern actually resembles his 2008 pattern more than anything.

This would lead to a question of whether it’s Burnett’s location of the curveball that’s problematic. In 2009, the pitch was swung at under 40% of the time and resulted in a strike nearly 60% of the time. In 2010, however, the swing rate has remained static, while the strike rate has dipped to a little over 51%. That’s not a radical shift, mind you, but a big enough one that it alters Burnett’s ability to succeed. If batters are able to hold off on the inevitable avalanche of curveballs that dive below the zone on two strike counts, that means Burnett will have to beat them with his fastball or sinker, a combination of which hasn’t resulted in a positive run value since 2007.

The most troubling statistic associated with Burnett is that 40% of his strikeouts have come against the Orioles and Indians. Those starts account for a little more than 20% of his starts this season.