Martin Perez will pitch game number 163 for the Texas Rangers. The 22 year old rookie left-hander is coming off his first season with significant time in the majors, after having gotten a 38 inning cup of coffee last year. He's pitched slightly over 160 innings this season, between the majors and the minors, which is the same amount he pitched last season (but more than in any season previous).
Here are Perez's 2013 major league stats, compared with those of his opponent tonight, David Price.
Perez has actually posted a slight reverse split this season, with a 4.16 xFIP against lefties (128 PAs) and a 4.02 xFIP against righties (380 PAs). That's likely due to his best secondary pitch being his changeup, although as I glance over his graphs, I wonder if he isn't actually throwing two distinct changeups, one with more sink and run than the other.
According to the Brooks Baseball classifications, Perez's four-seam fastball averages 93.6 mph, while his two-seamer sits slightly lower at 93 mph. Both his changeup and his slider average 85 mph, and his curve is at 77 mph.
Perez's curve is essentially a "show me pitch," which he drops in to get a strike against batters of both handedness and to slow down their bats. He throws more rising fastballs than he does sinkers overall, but he throws them both to hitters of both handedness. The interesting usage patterns come when you look at Perez's slider and his changeup.
Against the opposite-handed righty batters, Perez uses his changeup early and often (27%) while downplaying the use of his slider (8%). That's expected usage. Against the same-handed lefties, Perez will throw his slider 20% of the time, and his changeup 11% of the time. That's not unusual either, but what he does with two strikes is. Perez throws both his slider and his changeup a quarter of the time. He may not be comfortable throwing his changeup in early counts to a lefty, but he does still use it as an out pitch.
That's why I'm lukewarm about the Danks Theory in this case (Tommy Rancel, the original identifier of the practice, sees it as a possibility, but doesn't expect Maddon to sell out lefty either). Martin Perez's changeup is a weapon against hitters on both sides of the plate (near-40% whiff/swing rate), but it's his only real weapon to righties, and he has other good options against lefties (his sinker, slider, and curve all produce more frequent swings and misses, even if none of them match the rate of his changeup). Perez's reverse splits may simply be a matter of a small sample size or a rookie's struggles to adjust in the bigs. If he were to figure out that he can throw his changeup early on in the count to lefties, watch out.