Is Hellickson Getting Squeezed?

Jeremy Hellickson has been walking more batters this year (3.45 BB/9) than he did last year (1.98 BB/9). For a pitcher who's calling card is command, this is a lot (MLB average is around 3.3 BB/9). A quick look at his Fangraphs plate discipline numbers show that he's actually throwing slightly more pitches in the zone this year (47.8%) than last year (46.6%). Opposing players are swinging at less pitches (39.8% compared to 48.3%), and also whiffing less, which might indicate that he's not fooling players the way he did previously, but the decrease in swing rate is spread evenly between pitches in and out of the zone. If he has lost some trickery, I would have thought that it would show up more in the swing percentage outside the zone, not as a difference overall.

On the other hand, it's seemed to me that umpires are squeezing Hellickson, not giving him the called third strikes that more experienced control pitchers are rumored to be awarded. My first thought was to compare Hellickson's strike percentage with his zone percentage. And while he's in the zone more this year than last, he is in fact getting fewer strikes - 63.7% last year, compared to 59.5% this year. This doesn't, however, answer the question I'm trying to ask: Are umpires not awarding Hellickson strike calls on pitches in or near the zone that they gave him last year?

My second thought was that given that I'm sometimes called upon at work to act as a database analyst, and given the easy availability of good pitch f/x data, it's fairly ridiculous that I've never gotten set up to be able to answer that question for myself. After resolving to get the raw data when I went home and then not yet doing so, here's my third thought. Let's look at some pictures.

This Hellickson's location graph from last year.

via pitchfx.texasleaguers.com

And is the location for this year so far.

via pitchfx.texasleaguers.com

It's pretty clear to see that Hellickson isn't getting the calls on the bottom part of the strike zone the way he used, and the way Rays fans would like. Now I suppose that it's possible that there's a difference in pitch f/x calibration from year to year, or even that he's faced an abnormal amount of long-shinned batters so far in 2011, but the top, left, and right margins of those graphs look pretty similar to me, with only the bottom changing with the year.

I can't yet say why Hellboy is being gypped, or even if it's by enough of a margin to explain the whole rise in walk total, but he definitely is being squeezed this year, compared to last.