Marshall has only thrown 13 1/3 innings this season in the big leagues and has started just one game. So all the data I'm going to be pulling will be '07 data. He's turning 27 this year, so there shouldn't be any significant physical changes in his stuff. He may be a tick faster with the heater, but in all likelihood the only thing to change significantly at this point is control. So far he's managed 4.9 BB/G, so my guess is that hasn't happened. In addition, the '07 numbers came with Kalk's own pitch recognition algorithm, which I believe was replaced by Gameday's this year. Should be better than yesterday though, when Gallagher threw a change up I didn't even know he had. He only threw it once that I saw and his victim swung through it. So maybe it wasn't just me that wasn't expecting a change.
Additionally, you'll notice there's basically no data on lefties. He simply hasn't faced enough so far, so about all we can discern from it is pitch usage patterns. Looking at his '08 numbers, it does look like he may have canned his change. That wouldn't surprise me, as it wasn't a good pitch. To RHB, it was a waste pitch; he rarely threw it with two strikes and missed the zone with it almost half the time anyway. He almost literally never threw it to lefties. It had just a 5 mph difference with the fastball. That's just really ungood. So expect a fastball-slider-curve arsenal.
As of last year, he moved his fastball all around the zone and was pretty much average at finding the zone with it. The problem came when contact was made. A .375 BABIP and a .705 TB/BIP against RHB indicates an extremely hittable fastball. Even against LHB (where, remember, the sample size is small), he allowed a .300+ ISO. So if he's picked up an mph or two, it's still not going to be a good offering. Marshall is the sort of pitcher who can't afford to get behind in the count. His fastball is just not good enough to get away with it and throwing a lot of sliders to righties isn't usually a good idea. He generally got away with the sliders he threw, but in 2-0 and 3-1 counts, he threw the fastball at least two-thirds of the time. If his control is off, he'll have a very short outing.
The polar opposite of his fastball is the curve. It's almost exclusively reserved for counts when he's ahead, but it's deadly. He gets nearly 20% whiffs and the ISO against was .000 for RHB. I'd rather see the backward K than swings against this pitch, since the results are so poor. Unless it's a hanger, Sox batters really must lay off this pitch. Caveat: I haven't investigated our batters to know if any of them have good curve hitting skills.
The slider is below average from the whiff perspective, but he can throw it for strikes and gets decent in play results from it. The idea will be to limit the fastball use by getting ahead with this pitch. In fact, in relief appearances this year he threw it more than any other pitch including his fastball. It makes me wonder, for one, if he's got a cutter that's getting recorded as a slider and, two, if he can legitimately pitch off of it (rather than pitching off the fastball like nearly everyone else). He didn't record any two strike swings and misses from RHB last year with it, so I'm skeptical that he can do so if it isn't a legit cutter.
The problem with predicting how the Sox will do against Marshall is that he gets such divergent results from his fastball and curve. If he gets behind in the count, he's going to get crushed. Ahead, and he's got a devastating curve to rely on. He's similar in this regard to Gavin Floyd, who can get critical outs with a plus plus pitch. Perhaps it's saying too much of Marshall's curve though. I don't have the link, but KG compared Rich Hill and Sean Marshall, calling the former's curve great and the latter's merely good. On the other hand, Marshall is the one who's been a major league pitcher of late. It should make for an interesting matchup and not necessarily the slam dunk we thought it might be after yesterday's thrilling Q!-aided victory.