Back on April 30th, A.J. Burnett was sporting a nifty 2.43 ERA and had picked up three wins in his first five starts. After a dominant outing against the Orioles he talked about learning to pitch to contact, so we asked if he had altered his approach:
Traditionally a guy with a propensity to both strikeout and walk a lot of batters, A.J. has seen both of those rates drop to roughly 2/3 of their career norms. At the same time, he's given up more hits, is throwing slightly more strikes and is getting more outs on the ground.
About 3/4 of the pitches Burnett has thrown in 2010 have been fastballs, a proportion that he hasn't approached since his days with the Marlins.
Despite discovering his curveball somewhere along the way and tossing 7 1/3 strong innings his next time out, in his nine starts since then, Burnett's ERA is 5.50 and his record is 3-5. He's had four starts in which he's surrendered more than six runs, while in his first five outings the most he allowed in any outing was four.
A.J.'s still throwing over 70% fastballs, about 60% of all his pitches for strikes, inducing ground balls and allowing line drives at roughly the same rates (just under 50% and around 17%, respectively). So what has the difference been? Let's take a look at his rate stats:
Burnett's strikeout and walk rates have unsurprisingly returned close to his career norms and a slightly higher BABIP has led to an increase in hits per nine. But even all of those things in conjunction shouldn't cause his ERA to more than double. The real culprits (highlighted in red on the chart) are his home run and strand rates.
In 31 1/3 innings at the beginning of the season, Burnett had allowed just one long ball. In the 54 innings he's pitched since then, he's given up nine of them. To put it another way, he gave up home runs almost six times more often during his last nine starts than he did in his first five.
The league average stand rate is 72%. Burnett was very fortunate in that department early in the season but has been rather unlucky since. Of course, the fact that runners have stolen 19 bases off him and only been caught three times certainly isn't helping in that department.
Clearly, Burnett hasn't pitched as well since the beginning of May as he did before that. Home runs involve a certain amount of luck but a six-fold increase tells us that Burnett has been leaving plenty more balls out over the plate and hitters have been capitalizing on his mistakes. His strand rate has also been dragged down by all those long balls as well.
At the risk of stating the obvious, Burnett caught a lot of breaks early in April and saw his luck even out in a major way in the past month and a half. His home run rate won't stay as high as it has been and his strand rate will regress towards league average as the season continues. If you look at his expected FIP (based on batted ball types allowed) on FanGraphs, it's just about the same during his great stretch as it is throughout his awful one.
It's boring to say, and again this is pretty self-evident, but the true A.J. Burnett lies somewhere between the Cy Young candidate that showed up in April and the replacement level scrub that has been serving up 'tater salad since then. If he can lean just a little towards the former from here on in, he and the Yankees will be just fine.