There are a lot of reasons for A.J. Burnett's struggles recently.
Let's zoom in a little more closely on one reason for this-- the ineffectiveness of his curveball.
Burnett had major issues with his hook when he got shelled Saturday in Minnesota.
In one stretch in the second inning, Burnett threw nine straight curveballs for balls. That made it almost impossible for him to have any chance at success, as the Twins began sitting on, and subsequently hammering, his fastball.
This was actually a different problem than the one Burnett had been having most recently with his curveball.
My blogging colleague, Katie Sharp inspired this piece when she shared a note that in his first six starts out of the All-Star Break, Burnett allowed 15 hits with his curveball.
Major League Baseball employs a pitch-tracking system known as Pitch F/X in all 30 parks. It allows for the measurement not just of pitch velocity, but of how much the pitch breaks.
Sharp's lookup showed that Burnett's curveball went from having a six- inch vertical break at the start of the season, to a four-inch break over the run leading up to the Twins game.
Where can that be seen?
Our pitch tracking system allows us to break the strike zone up into nine equal pieces. The center square in that grid is what we call the "middle-middle" part of the strike zone.
The average major league hitter likes that kind of curveball. When he puts it in play, it results in a hit about 35 percent of the time.
Prior to the All-Star Break, Burnett threw a lot of curveballs, and very rarely did he throw one middle-middle. Hitters saw about one per game.
Since the break, the percentage of Burnett's curveballs that ended up middle-middle doubled. Hitters began to see three or four such pitches per game.
Burnett paid for this. The Rays had a couple of hits against pitches to that spot in Burnett's first start out of the All-Star Break. He gave up a couple more in that start against the White Sox in which he couldn't complete five innings with a huge lead. Derrek Lee dinged Burnett for a double in his most recent start against the Orioles. In all, he gave up seven middle-middle hits in this eight-start stretch, after yielding only two all season.
That's a small piece of the Burnett puzzle, but it's an important one, because of how much Burnett relies on his curveball to get outs.
In arguably his three best starts of the season, against the White Sox on April 25, the Royals on May 11, and the Indians on June 13, Burnett got 27 outs with his hook and yielded just one hit.
He threw only one curveball in those three games that was middle-middle in location. The pitch had an average break of nearly six inches and most frequently landed in the lower-third of the strike zone, or just below.
The average big league pitcher gets swings-and misses on curveballs in the lower-third of the strike zone nearly 40 percent of the strike zone. But the key is to make the pitch tantalizing.
Take a look at the three heat maps below that close out this piece. They show the difference between the three types of curveballs that Burnett has shown this season (for our purposes, the side of the plate for the hitter is not pertinent)
The one on the left: This shows where Burnett located his curveball most frequently in his July/August slump. Those pitches are too high for him to have any success.
The one on the right: This is where Burnett threw his curveball most frequently against the Twins. Those pitches are not close to a spot where a hitter would want to swing at them.
The one in the middle: This shows his curveball location from his three best starts of the season.
In short, that's where Burnett would probably want to put his hook tonight. Should he not do so, he may face a starting rotation hook sooner rather than later.