After reading Tony La Russa's comment about Zach Duke last night (according to DK, he told reporters, "You saw Duke pitching, right?" when asked why his hitter struggled last night), I decided to go in to the PitchFX and look around a little bit to see if I could find more of an explanation than "he's throwing a little harder this year" to attribute his turnaround to. I mean, he is throwing a little harder, I think (I haven't really compared, but last night Pitch FX spots his fastball right around 89 all night), but there's got to be more to it, right?
The first thing I noticed on the graphs from last night is how nasty his curveball looks against right-handed hitters. I pulled up the full chart with pitches and outcomes and sorted the changeups. There are two that are misclassified fastballs (I think), so that leaves us with 12 pitches, all thrown to righties. He threw ten for strikes (both balls were to Pujols) and of those ten strikes, two were fouled off, four were hit for ground outs, three were swinging strikes, and one was a called strike. That's a really good pitch.
Next up is the curve, which he threw 30 times for 19 strikes. Those 19 strikes resulted in four foul balls, seven called strikes, two swinging strikes, two groundouts, a flyout, and a single. In total, he went to his change or curve 42 times with only 13 balls. Of the 29 strikes, only six were put in to play and only one of those went for a hit. I don't have time to compare this with a start from last year (I will at some point soon, I hope), but those numbers strike me as being really, really good.
Still, we at least partially have an answer; it's not just an improved fastball that's making Duke better. He's throwing some really good off-speed stuff as well.