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Breaking down Pujols’ declining slugging percentage

What Albert Pujols is swinging at, where and resulting contact rate leads to a lower slugging percentage in 2010.

Pujols' home run (AP Photo/Lenny Ignelzi)By Ian Walton

A popular topic of conversation at The Cardinal Nation Blog has revolved around Albert Pujols’ declining slugging percentage.  The following article will attempt to demonstrate that this is likely a result of Pujols being less selective in which pitches he hits.

There is little doubt that Pujols has lagged behind his normal power production this season.  His .570 slugging percentage lies somewhat below his career .625 mark and noticeably below his .653 and .658 rates in 2008 and 2009.  In 2010, he is hitting home runs every 5.3% of his at-bats and doubles at the exact same rate.  Compare that to his career rates of hitting a home run in 7.1% of his at-bats and a double in 7.5% of his at-bats.

Year % Swinging Outside Zone % Contact Outside Zone % Swinging Inside Zone % Contact Inside Zone % Pitches Thrown Inside Zone
2007 18.3 72.3 59.0 93.9 49.9
2008 21.6 75.1 63.8 95.8 47.1
2009 22.9 68.2 66.6 94.4 45.0
2010 28.3 76.5 65.2 88.6 43.7
Career 19.8 66.1 65.6 92.1 49.1

As can be seen above, opposing pitchers have been throwing fewer pitches within the strike zone to Pujols in each of the past four seasons.  This is certainly understandable behavior, as Pujols is unquestionably one of the strongest hitters in the game today.  However, in each of the past four seasons, Pujols has increased the rate at which he swings at pitches thrown outside of the strike zone, with 2010 showing a dramatic increase over years past.  Somewhat surprisingly, he has actually increased his contact rate at balls thrown outside of the strike zone this season as well.

The above graph displays the location of each pitch thrown to Pujols in 2010 that resulted in a home run from the perspective of the catcher (except for his home run on 6/15, where data is for some reason not available).  Aside from one high four-seam fastball, these pitches are located in the center portion of the zone vertically and the outer half of the plate.  Not a single home run was hit outside of the strike zone.

So in summation, opposing pitchers are throwing Albert Pujols fewer strikes while Pujols is swinging at more balls.  As he is only hitting home runs on balls thrown to a particular portion of the strike zone, he is understandably hitting for less power this season.

Swing Rate data was provided by FanGraphs.
Pitch F/X data was provided by Brooks Baseball (though the graph is mine this time).

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Brian Walton

Brian Walton runs The Cardinal Nation and The Cardinal Nation Blog, covering the St. Louis Cardinals and minor league system.
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