Adrian Gonzalez’s Evolution, Part I

This is the first of a two-part series on Adrian Gonzalez’s evolution as a hitter.

Writing for ESPN.com last year, Dave Cameron suggested that then-newly-acquired slugger Adrian Gonzalez was displaying a new approach at the plate in Boston. Cameron pointed out that, as of May 14, Gonzalez had significantly reduced his walk percentage (BB%) and increased contact on pitches outside the strike zone (O-Contact %). Like 2010, Gonzalez was back to swinging at more pitches, but was making contact on roughly 85% of his swings. That was a huge jump from his carreer average at the time.

Since we’re on the cusp of a new season, I thought it’d be interesting to revisit Gonzalez’s 2011 to see if those early season trends held for the entire year. Overall, Gonzalez put up a .406 wOBA in 2011, versus a .378 with the Padres in 2010. The smooth-swinging first basemen got on base more often and also slugged for a higher percentage —though his ISO numbers were nearly identical. So the question is this: Was his 2011 success due to a different approach?

To figure that out, I created a series of heat maps based on Pitch F/X data that compare Gonzalez’s performances in 2011 and 2010. For the first part of this series, I’m only focusing on his overall performance. In the second part, I’ll take a deeper look and mine his home-road splits.

The first thing we need to check on is whether opposing pitchers took a different approach with Gonzalez after his move to Boston. As the data suggest, pitchers didn’t appear to approach Gonzalez all that differently:

There are some small changes in certain zones, but pitchers were pretty consistent with Gonzalez. Even if you break out fastballs from off-speed pitches, the percentages are basically the same by zone between 2010 and 2011.

Despite the season-to-season similarities, though, we see striking differences in the slugger’s approach in different zones.

Gonzalez didn’t swing at more pitches in 2011, but he did alter what pitches he went after. The graphic below shows the difference between Gonzalez’s swing percentage from 2010 to 2011 in various zones:

We see that Gonzalez offered at more pitches on the outside of the plate, as well as down and in, and overall appeared to expand his zone in 2011. This is consistent with what Cameron observed last year. In addition to expanding his zone, Gonzalez increased his contact rate (Contact %) considerably from 78.7% in 2010 to a career-high 81.8% in 2011. The graphic below shows the difference in Gonzalez’s whiffs-per-swing in each zone between 2011 and 2010:

Looking at pitches on the outside of the plate — as well as pitches up in the zone — Gonzalez dramatically reduced his strikeouts. But did his change in swings translate to his performance?

The graphic below shows the difference in Gonzalez’s wOBA per swing in 2011, versus 2010, for different zones:

It seems we have our answer: Gonzalez raised his overall production relative to 2010 (153 vs. 143 wRC+), but here we can see exactly how he increased his production. Despite hitting the same percentage of batted balls the opposite way (28% in 2011 versus 28% from 2008 to 2010), Gonzalez increased his wOBA/swing by .087 on pitches up and away. He also  jumped roughly .035 on belt-high and low pitches on the outer half of the plate; he went up .097 on balls that were up high or in the middle of the plate; he increased his wOBA/swing by .062 on pitches belt-high and inside; and he saw a .049 jump on pitches down and in.

What’s interesting here is that Gonzalez increased his wOBA/swing on belt-high, inside fastballs by .062; but he actually decreased the number of pitches he swung at in this zone. If Gonzalez became more aggressive on outside pitches then that might have allowed him to be even pickier on pitches that were inside. And pitches that he may have avoided earlier because he was less productive on contact suddenly became much more productive, which freed Gonzalez to take a hack, rather than risking a called strike.

So what have we learned? At a high level, the data suggest that while pitchers didn’t appear to have altered their approach with Gonzalez, he still evolved at the plate. Gonzalez seems to have expanded his zone on the outside and around the letters — and he dramatically reduced the number of pitches on which he whiffed. What we don’t yet know is whether his performance change is attributed to the dimensions of Fenway Park, relative to Petco. Was Gonzalez emboldened, as Cameron suggested, by Fenway’s hitter-friendly confines — especially the Green Monster? To untangle this, we need to compare the difference in Gonzalez’s performance using home and road splits. If Cameron was right, we should see that Gonzalez’s appetite for balls on the outer half of the plate in 2011 was more prominent at home than on the road, especially when compared to 2010.

I’ll take a look at that in the series’ second part.