Will's post about Joakim Soria not missing any bats this year led to a side conversation about whether or not he's throwing a cut fastball this year.  At first, I questioned if it was a classification issue because it's one of the first things that always pops up whenever Pitch F/X is says someone is throwing a new pitch.  Jeff Z shared this nice graphic from Brooks Baseball showing his pitches from his last outing.

via assets.sbnation.com

To my untrained eye, it looked like a fastball with less velocity.  Seemed like a cutter should have a slightly different spin axis. These are all in the same area, the pitch just moves a little slower.  So I took to twitter to get in contact with Pitch F/X guru Mike Fast.  He kindly replied with the following:

Soria throws 4 pitch types: fastball (call it a cutter if you want), changeup, slider, curve.  His fastball is normally ~91 mph.

When this was posted, I was instructed to specifically mention the speed differences.  Mike was kind enough to reply again:

There's a hint he's throwing his fastball at two different speeds this year, ~90 mph and ~86 mph, but I don't know what to make of that yet.

Second Reply: I'm not sure if it's a purposeful strategy by Soria or a case of inconsistent mechanics/injury.  Movement's not changing, just speed.

After patting myself on the back, I looked at a few other pitchers that are known to throw cutters to see how they react compared to fastballs in the same graphs Jeff shared. 

First up, the cutter king Mariano Rivera

Fastball and cutter have a different spin angle, Soria's pitches in question do not.  Searching for other pitchers that throw a cutter, I found this thread and picked out Scott Feldman and Angel Guzman for two more guys to look at quickly.

Feldman

And Guzman, though it needs to be noted that both Harry Pavlidis and Mike Fast classify this slider as a cutter.

If his slider is really a cutter, (which makes sense when comparing the speeds and spin angle to the other charts) then both of these guys also show a slightly different spin on their cut fastballs than on their regular fastballs.  That's just something that we can't see with Soria's pitch yet.  However, he could be trying to take some of the heat off in an effort to get more movement on the pitch.  While looking up some info on this, I came across this post by Mike Fast about Soria from May of last season.  Fast says:

Soria has a fastball with a lot of cut that runs 89-94 mph. The cut fastball is his bread-and-butter pitch; he uses it for 69% of his pitches to lefties and 78% of his pitches to righties.

Of course, he also includes this nugget and it's a huge difference from the pitcher Will noticed:

Soria gets a lot of swinging strikes in the zone to both lefties and righties.

I don't know enough to be able to choose a side and this was too long for a comment, so I shared here.  But if I had to pick a side, when dealing with Pitch F/X it has to be with the non-RR guy.  Sorry Jeff, no hard feelings.  As the season goes on, the answer should become a little clearer.