Have pitchers adjusted to Mauer?

In efforts to explain the drop-off in Joe Mauer’s home run totals from 2009, Bloomberg Sports, an outstanding analytical entity, offers yet another theory: Pitchers are adjusting to Mauer.

Maybe pitchers are attacking Mauer differently too. This argument could potentially explain some of the catcher's power struggles. Pitchers, in fact, have been unwilling to throw him fastballs in certain counts, and seem to have replaced them with changeups, and occasionally curveballs.

Abstaining from throwing fastballs to the league’s best fastball hitter in 2009 would seem like a fairly good place to start if you were attempting to subdue his offensive onslaught. After all, Mauer swatted 27 of his 28 home runs leading to an AL-best .691 slugging percentage on fastballs. Nevertheless, at first blush, the repertoire used against him in 2010 is strikingly similar to the strategy deployed on him in 2009. Using the numbers supplied at Fangraphs.com, we find that opponents are tossing fastball at him most than 60% of the time mixed in with sliders and changeups augmented by the occasional curve. This is fairly consistent with the career norms.

However, like the article from Bloomberg indicates, once we dissect the individual pitch selection during specific counts, it reveals a much different tendency this season. For example, during the 2-1 count, a situation where a year ago Mauer slugged 9 of his 28 home runs, the catcher was thrown 4-seam fastballs half of the time. This year, pitchers have toned down the amount of straight fastballs to him:

2-1 count	4-seamer	2-seamer	Slider	Change	Curve
2010	43%	12%	10%	17%	3%
2009	50%	5%	15%	12%	7%

(via pitchfx.texasleaguers.com)

When you consider the success he had against 4-seamers in his career - particularly during a hitter’s count such as this where you would expect a fastball - the decision to alter the approach makes complete sense. Though it might not seem like much, the additional movement and variation in velocity has kept the reigning MVP from getting the same loft on his swing as he did the previous season. Last year Mauer hit fly balls 42% of the time during 2-1 counts but this season he’s lifting only 15% of balls in play in this situation. Likewise, the different look has enticed Mauer to turn the ball over more frequently, hitting groundballs 60% of the time.

Similarly, during the 1-1 count in which Mauer also launched another 4 home runs last year, pitchers are reluctant to feed him as many 4-seamers, instead changing speeds with more changeups and curves:

1-1 count	4-seamer	2-seamer	Slider	Change	Curve
2010	39%	8%	12%	17%	10%
2009	47%	3%	16%	15%	8%

(via pitchfx.texasleaguers.com)

Also, in efforts to disrupt his timing, pitchers have started him off with more curveballs:

First pitch	4-seamer	2-seamer	Slider	Change	Curve
2010	51%	9%	7%	7%	11%
2009	59%	4%	11%	7%	5%

(via pitchfx.texasleaguers.com)

This has seemingly kept him from pouncing on the first pitch for a home run as he did three times last year.

To be sure, there is no one reason as to why Mauer's home run totals spiked so suddenly in 2009 and dropped so dramatically this season. It has most likely been a concoction of several factors. As the writer at Bloomberg Sports pointed out, it appears that Mauer is no longer afforded the luxury of jumping on straight fastballs like he did in hitter’s counts last year. This - combined with Target Field’s home run restrictive nature (5th least home run conducive ballpark in MLB) and a regression to his career home runs-to-fly ball rate - provides some insight as to why the Twins catcher has been unable to pepper the bleachers thus far in the season.