There was some kind of error with one of the Heyward at-bats as the data didn't show up, so I tossed it (along with any other data sets that had errors). Using the data from baseballsavant.com, here is how Marcum's locations break down by zone:
average zone in 2013: 10.13
average zone on Sunday: 9.82
average zone in 2012: 10.48
average zone in 2010-2011: 10.34
It doesn't seem the zones are predictive for what was wrong, or what went right for Marcum on Sunday, or even the difference between 2010-2011 and 2012. So what about release point? Here we can see a clear change:
Average vertical release point in 2013: 6.3
Strangely, despite some shoulder injuries, his release point is creeping up. It isn't what was predictive for what went right on Sunday, and is only really predictive from year to year in a reverse way, meaning it seems that you would have to believe that the higher release point is worse for Marcum. I think it is just descriptive of him changing, but not really prescriptive of success.
Average Horizontal release point in 2013: -.82
Just like with the vertical release point, Marcum has been moving to what you would call a more ideal place, closer to the center of the rubber. Again, it is unlikely that this is making him worse.
Velocity has never been a key part to Marcum's game, but it is helpful to look at how hard he is throwing anyway (using the traditional 50 feet from home plate measuring stick, instead of the Brooks Baseball way of 55 feet, which makes the velocity tick slightly up). Here is what his velocity has looked like so far this year (broken up by pitches, unlike the rest of the graphs):
Here is what it looked like on Sunday:
In 2012, he saw a clear decrease in velocity:
So in conclusion, velocity drop seems to be the most likely explanation for why he is no longer the 3 win pitcher he was in 2010-2011, though there is a location explanation as well. According to Baseball Heat Maps, Marcum threw pitches on the "edge" of the plate 15.9 % in 2012, similar to A.J. Burnett and Chris Sale (257th out of 659 pitchers). Marcum had a 17.6 Edge % in 2010 (88th) and 15.7 % in 2011 (315th). According to Bill Petti, he has a 15.5 Edge % so far in 2013. So it seems that he is working on the edge of the plate a little less than he had previously, which could, if you buy into the philosophy behind that data, explain his high BABIP in 2013. As far as 2013 goes, I think Marcum can still be an effective pitcher. I don't think he is quite as good as his FIP and fWAR says he is because I believe the home run rate will regress back to career norms (and even his non home run DIPs like kwERA at 3.47 currently, will probably regress as well), but he can still be a good starting pitcher, the question is whether or not he will be healthy or not.