Note: I originally posted this on my blog before his most recent start, but I was hoping I could perhaps get some feedback.

Lost amid much of the early-season trials and tribulations of this year’s Yankees squad has been the performance of the Yanks’ lead pie-thrower, A.J. Burnett. While Burnett can boast of an improvement in his walk rate (3.11 BB/9 in 2010; 4.22 in 2009; 3.75 career), his strike-out rate has seen a steeper drop (2010 K/9: 6.43; 2009: 8.48; 8.27 career). David Golebiewski of FanGraphs recently wrote an article in which he pointed out that hitters are making much more contact this year than in past years off of Burnett. Golebiewski posited that this was due to the ineffectiveness of Burnett’s knuckle-curve, but I believe that Burnett’s diminished fastball velocity and overall approach to pitching has also played a role in making him more hittable. Here are Burnett’s velocity charts:

In 2007, the first year in which velocity data was available from Pitch F/x, Burnett was averaging 95.9 MPH (the gap you see in the velocity chart can be explained by a two month-long stay on the disabled list for a shoulder strain). In 2008, Burnett’s velocity saw a rather large drop to 94.4. The velocity held steady in ’09, when he averaged 94.2 on the fastball. This year, however, Burnett’s velocity has dropped down to 93.2.

There are two possible explanations for Burnett’s decrease in velocity. It is very possible that Burnett is toning down his velocity in order to have better command, and the decreased walk rate appears to indicate that. The decrease in overall fastball velocity could also do with the fact that Burnett has added a two-seam fastball to his repertoire, throwing it 25.1% of the time, in comparison to his four-seamer, which he throws 46.8% of the time. As a side note, the four-seamer and the two-seamer have similar velocities (4-seam: 93.3; 2-seam: 93.1).

Apparently, Burnett has adjusted his pitching philosophy. He has spoken of his wishes to “become more of a pitcher” (Mark Feinsand) and to “pitch to contact” (Chad Jennings). Developing the sinker seems to go along with that thought process. Catcher Chad Moeller, as quoted in the Jennings piece, indicated that the two-seamer away to left-handed hitters was intended to induce more groundballs. Indeed, it has. In 2010, Burnett has posted his highest ground-ball rate against lefties (51.1%) since 2007, when it eclipsed 53%. Overall, Burnett is inducing ground balls at a rate of 48.4%, which is good, but not great.

Usually, it’s good to have a third pitch, especially if you are a starting pitcher. I laud the fact that Burnett has started using a two-seam fastball and is trying to be smarter about pitching, but the overall approach that he has adopted this year has robbed him of his gargantuan K rate. The meager improvements in walk rate and ground-ball rate are not enough to justify losing nearly 2 K/9 innings. Keeping balls on the ground is great and all, but the strength of Burnett’s game has always been inducing swings and misses. Getting away from his bread and butter does not appear to be working.