Here is the AFL rising stars box. Fabio pitched the 5th, sitting 93-96+97 on his fastball, much as he has all season. Ben Revere saved a run for him making an outstanding catch, running into the CF wall, after Castillo had a slider crushed. His next 2 outs were groundouts on the same pitch. He didn't throw a single changeup, which is actually his #2 pitch. Castillo wields an impressive groundball rate of 3.2 his first AFL stint and I would imagine that working on his breaking ball (which used to be a curveball) has been a big part of his winter work.
He is a lock for the 40 and could quickly make it to AAA in 2011 after only making a few appearances in AA in 2010. They key for him is maintaining consistent mechanics which he and the Texas staff managed to iron out for the first time in 2010.
Jason Grey has some nuggets on the game for Insiders (while Castillo gets no mention at all from Keith Law). Here is his note on Castillo, which is notably more pessimistic about his mechanics than anyone else has been this year. It is almost like Grey is talking about Pre-2010 Castillo when his weird mechanics were an issue without addressing the reasons for his progress this year (assuredly some mechanical adjustments). Grey's note on the possibility that Castillo's delivery makes him a legit injury risk is the first I've heard anyone make such an unequivocal statement:
I was also asked about Texas Rangers reliever Fabio Castillo, who "really came into his own this season," according to one scout I talked to who follows the Rangers' system extensively. Castillo has been between 94 and 96 mph and touched 97 multiple times here at the Fall League, and the 21-year-old righty struck out 65 in 51 2/3 innings, walking just 26 and allowing just two homers, in a tough pitching environment in the Class A Cal League this past season. Castillo's fastball has good late movement, running in on right-handed hitters. I've heard he calls his breaking ball a hard curve, but it looks more like an 86-88 mph slider that projects to be a solid-average pitch. He also throws an 86-88 mph straight changeup that he will occasionally tip by slowing his arm speed, though he does throw strikes with it. The negatives are that Castillo has below-average command of his fastball right now, and his delivery is scary, flying open as he whips the ball toward the plate with a huge amount of recoil and a ton of stress on his arm. It's intriguing raw ability, and he profiles as a potential setup man for fantasy purposes, but it's hard to see his arm staying healthy over the long haul with those mechanics.
Chatting with Jason Cole over at Lonestar Dugout about Castillo and he mentions that Castillo's breaking ball is indeed his second pitch at the moment, as opposed to his changeup. He also notes that his breaking ball has a different shape to it now than in the beginning of the season. Cole is planning on interviewing Brad Holman this week - Castillo's pitching coach in Hickory in 2009 - who will likely provide some insight into Castillo's nice 2010. Check out Jason's site (fee based, with some free content) if you haven't already.
As a side note, I have been impressed with the amount of sliders and changeups that Castillo has mixed into his ~7 AFL outings thus far, though he didn't throw any changeups in the Rising Stars game. In the AFL games with pitch f/x, both pitches have missed bats and induced groundouts, with an excellent GO rate (SSS to be sure). In his last few outing his strike rate hasn't been that great, but his ability to induce grounders has enabled him to get out of innings with a low pitch count and he can still dial it up to 97 when he needs to.
As a caveat, the significance of AFL #s shouldn't be exaggerated, for hitters or pitchers. They are by definition short sample size and the AFL is also a place where players are working on aspects of their game per the instruction of their parent club with the cooperation of their respective AFL coaching staff. If I had to guess, Castillo's AFL homework included mixing in his changeup more, even to the detriment of his #s (but to no ill effect so far), keeping the FB low in the zone, and inducing groundball outs. How these things are interrelated with his mechanics, I can't be sure. It will be interesting to see what Holman has to say about the nature of Castillo's progression over the course of the last year: does he have a new breaking ball, a new grip? Why has his change been more effective, mechanics, a new grip? Why is he now more consistent with his FB command and velo?