A week and a half ago, it became evident that Julio Mateo was trying out a new arm slot in an effort to increase his effectiveness by getting sharper break on his slider. It sounds small, but an adjustment like that can make the difference between being a passable middle reliever and being Julio Mateo, so it was worth trying out. This wasn't just a case of Dave, Jason Churchill, and me seeing what we wanted to believe, either - the adjustment was confirmed by Rafael Chaves, who wanted to see Mateo improve his breaking ball.
Here's the problem with mechanical adjustments, though: they're very, very difficult to make. A pitcher who's been throwing a certain way his whole life will have that particular delivery engrained in his muscle memory, and overcoming that takes a lot of time and a lot of work. They're certainly doable, but the point is, talking about making a change and working on it in the bullpen doesn't automatically mean it's going to work out like the coach and pitcher want it to. Changing a delivery isn't easy.
Which brings me to Julio Mateo last night:
On the pitch to Michael Young that, for all intents and purposes, ended the game, we see Mateo completely reverting to his old arm slot. There's no sign of any adjustment; he looks exactly the same as he did earlier in the season, shoulders tilted and elbow bent. The pitch subsequently got destroyed.
It's been observed that, in high-pressure situations, a pitcher will use whichever throwing motion is most comfortable. What this means is that, if you have a guy who's just recently made a change, and you bring him into a big situation (say, bases loaded in a one-run game against one of the better offensive middle infielders in the league), he's likely to revert back to his pre-adjusted delivery, because he's not comfortable using something new and experimental when it might result in a bad outcome. And that seems to be exactly what we see in Mateo's case. In a high-leverage situation in which he had little margin of error, he went back to his usual arm slot because that's how he felt most comfortable going after Young. It's not Mateo's fault; that's just how a pitcher's brain (and throwing muscles) are wired.
This is why I'm not a big fan of mid-season mechanical adjustments. Not only does a pitcher have less time to work in the bullpen and concentrate on one particular facet of his delivery, but he's also at risk of stunting (or even erasing) his progress by being brought into a situation he's not ready to face. If you've recently made a change in your throwing motion, then you slip up and revert back to the old one, you're only reinforcing the old muscle memory and negating a lot of your improvement, so unless you're really really really focused on staying consistent with the change, the whole process is going to take a long time (if it works at all).
The only way to make a midseason mechanical adjustment pan out the way you want it to is to ensure that the pitcher in question isn't working in high-leverage situations where he's likely to experience a setback. You can bring him in as a middle reliever, go to him as a mop-up man, or even temporarily demote him to the minors (see Gil Meche, Joel Pineiro, Roy Halladay, etc.), anything to make sure that he can concentrate on his delivery without being too concerned with the immediate results. With enough time and effort, you can make it work in several weeks to a few months.
What you can't do is make a change and then ask the guy to get critical outs in high-pressure situations. Bryan Price was constantly tinkering with Gil Meche during the season, but for much of the time Gil was pitching out of the rotation, and that's a stressful job, so the returns weren't anywhere close to what the coaching staff was looking for (it should also be noted that Price never gave him enough time before moving on and trying something else). The change that finally made Meche a little better appears to be something he worked on during the winter, when it's so much easier to make a long-term adjustment. This isn't a coincidence.
Julio Mateo and Rafael Chaves can work on improving his delivery all they want, but if Mike Hargrove doesn't cooperate by limiting him to the mop-up role he deserves, it's almost certainly not going to do anything, at least not until the season's over and Mateo can work without worrying about what's going to happen. The whole arm slot thing seems to be going the way of Roberto Petagine - right idea, wrong environment.