Josh Collmenter: Dominant Reliever, Mediocre Starter

Since coming up to the big leagues in 2011, Josh Collmenter has been used in a variety of roles by the Diamondbacks. The right-hander known for his extreme over the top delivery has been much better as a reliever than a starter. Rather than the normal (2013 so far) split of 4.06 kwERA and 2.85 HR % as a starter and 3.84 kwERA and 2.48 HR % as a reliever (.22 kwERA and .37% difference), Collmenter has a career 3.97 kwERA and 3.3 HR % as a starter, and 3.13 kwERA and 1.48 HR % as a reliever (.84 kwERA and 1.82 HR % difference).

As a starter, Collmenter's average release point is  -.48 horizontal, 7.18 vertical and here is what his Spin and Speed Chart looks like:

He sure seems easy to classify, but the MLBAM tags have problems with the fastball and changeup differentiation so I classified his pitches myself using the chart as a guide:

average pitch 84.25 MPH
Fastball: 87.97 MPH
Change: 77.50 MPH
Spin Curve: 70.35MPH
Non-Spin Curve: 70.49 MPH

Collmenter's big platoon splits (4.36 kwERA and 2.96 HR % against lefties, 3.17 kwERA and 2.79 HR % against righties) seem weird since he throws straight over the top and throws a lot of changeups. 

Here are his average locations as a starter, broken down by pitch:

 

He doesn't work on the arm side part of the plate like most right-handed pitchers do, instead working right down the middle of the plate. The fastball is thrown in the high part of the plate, and with that velocity, it is easy to see how that would lend to some power. The high spin curve is thrown lower than the regular curve on average, and his average pitch overall is thrown right down the middle.

As a reliever, Collmenter's average release point is -.36 horizontally, and 7.23 vertically, so a little bit higher and closer to the center (though nothing real drastic). Here is what his pitches look like as a reliever:

It seems that the difference in  spin between the fastball and changeup lessens in the bullpen. That may mean nothing, or it may mean that they are tougher to distinguish for a hitter trying to guess. Here is the breakdown of his pitches:

Average Pitch: 85.1 MPH
Fastball: 88.17 MPH
Change: 77.98 MPH
Spin Curve: 71 MPH
Non-Spin Curve: 71.32 MPH

So on all pitch types, Collmenter actually has gained less velocity on average than most pitchers who move from the rotation to the bullpen (or vice versa). I think velocity doesn't have much to do with his splits from the bullpen to the rotation, as he is well below average as a starter and well below average as a bullpen pitcher. So how about location differences?:

The spin curve is thrown out of the strike zone (and is a little more rare), while the regular curve is actually thrown much higher than as a starter. His fastball is at about the same height, but actually a little glove side. Other than the change, which is a little more arm side, his pitches go a little more glove side on average.

There is always the chance that as a starter he is just a victim of his home ballpark or the home run rate is just due to regress. The locations are different, especially with the fastball versus the changeup as a reliever, and this may give him a little more deception and help him avoid power more. But, other than that, it is a little hard to see the difference in Collmenter as a reliever and as a starter, so I wonder if a lot of the difference in numbers is small sample statistical noise.