Predictable Burnett

A.J. Burnett of the New York Yankees produced an interesting fastball graph this season.

A.J. Burnett fastball over time, 2011.Note that over the course of this season, his fastball velocity stays very even.  Batters, however, swing at it less.  Their contract rate remains the same, but they are producing a higher average when they hit the ball.

I have a bit of a background in machine learning.  This kind of improved output over time from a learning algorithm would make the programmer very happy.  Batters have learned to recognize the fastball when to swing and when not to swing, and that's leading to more balls falling for hits.  You can especially see this in counts where A.J. holds the advantage over the hitter.  In April and May, batters hit .218 against Burnett's fastball in pitcher's counts with a .251 wOBA.  Since then, his BA allowed is up to .318 in those situations with a .286 wOBA.

Burnett's fastball became predictable, and batters are taking advantage.

A.J. Burnett's 2010 Fastball

A.J. Burnett Overall

	AVG	OBP	SLG	wOBA
2009	.250	.338	.401	.334
2010	.285	.363	.457	.367

A.J. Burnett vs. LHB

	AVG	OBP	SLG	wOBA
2009	.222	.312	.352	.303
2010	.286	.373	.444	.368

A.J. Burnett had a much tougher time against left handed batters in 2010 than in his first season as a Yankee. In addition to the jump in his overall line, Burnett's K-Rate against LHB dropped from 24.9% in 2009 to 16.2% in 2010, striking out 43 fewer.

One thing that stood out was the drop in effectiveness in A.J.'s fastball in 2010, particularly against lefties.

A.J. Burnett's Fastball vs. LHB

	PA	AVG	SLG	wOBA
2009	274	.276	.474	.378
2010	190	.371	.648	.472

A.J.'s 2010 fastball averaged 93.2 MPH, a loss of 1 MPH from 2009. He was also much less effective in throwing the pitch down and away to LHB in 2010.

A.J. Burnett's Fastball vs. LHB 2009
A.J. Burnett's Fastball vs. LHB 2010
A.J. Burnett's Fastball vs. LHB (Highlighted Zone)

	PA	AVG	SLG	wOBA
2009	83	.250	.325	.271
2010	52	.298	.489	.378

In addition to the drop in velocity, Burnett's fastball also lost some downward movement. In 2010, his fastball was dropping at a rate of 11.6 ft/sec as it crossed the plate, about 4% less than 2009. This loss of movement combined with a drop in velocity may have contributed to his reduced K-Rate to lefties, and decreased the effectiveness of his fastball down in the zone.