Too often the question we ask about pitching prospects is "when?", before we bother to consider "if...". Wily Peralta had it all coming into the 2012 season. He tore up AA and was even better in his brief stop in AAA in 2011. He always had great velocity, a sturdy frame, and little concern about his durability. Some hoped that he would make the rotation out of spring training this year, and even people like me saw it as a matter of time before he forced his way into the major league rotation.
Then, as it so often does, baseball messed everything up. Peralta's walk rate per 9 innings jumped from the mid-3.5 range of 2011 to 4.8 in 146 innings in AAA. Was 2011 the outlier? Who knows. What we do know, however, is that he's been awfully impressive in his 2-start audition for next year's rotation, and that at AAA he had a very rough start to the season but has been on a trend towards better performance.
First let's step back and look at his raw stats through 2 starts.
6 innings, 4 BB, 3 K, 5 hits, 3 ER
6 innings, 1 BB, 4 K, 7 hits, 1 ER
I've been able to see most of both starts and have to say he's just flat out looked impressive. He's been able to get groundballs (especially last night, and 59% this year in 13 innings is quite high), and he's been able to get strikeouts when necessary. The best example of this, of course, was his final two batters last night. With 1 out in the sixth, a runner on first, and the Brewers down 1-0, Peralta had to face Jason Heyward and Chipper Jones. Heyward's at-bat went like this:
Peralta gets behind 2-1, then Heyward fouls off a fastball at 96, a slider at 85, and a fastball at 97 before Peralta throws him a nasty slider just inside at 87 and Heyward goes down swinging. Next up is Chipper Jones:
Peralta misses outside badly with a changeup and a slider, then can't find the zone with a 2-0 95 mph fastball and every Brewer fan everywhere held their breath. I think fans not even watching the game probably sensed that something disturbing was about to happen. But Peralta fired a 93.5 mph fastball, one of his slowest on the night, that apparently just caught the outside edge. Chipper swung and missed at his next 95 mph fastball, pretty much down the middle. Then he surprised him with a 87 mph slider to catch him looking and end the inning.
Peralta's success as a Brewers starter is going to depend primarily on one thing, and that is his changeup. He's used it sparingly so far in the big leagues, throwing it only about 8% of the time. It's a heck of a nasty pitch if he maintains consistent arm action, though-- it averages about 85 miles per hour, and his fastball near 96, and that 11 mph gap is larger than an average split and is tougher for hitters to adjust to.
We've seen the nastiness of Peralta's slider, and as the two at-bats above show, it could be deployed as an effective weapon against lefties. It's something of a rarity to see a 2-pitch pitcher develop into a front of the rotation starter (obligatory Ben Sheets reference), but Peralta seems to be right there on the cusp.
I see two paths forward for Peralta, and I don't know enough about him, or scouting, to tell you which one his career will take. If he develops enough control of the changeup to at least keep it in the back of a hitter's mind, he could be a solid mid to upper-level starter for years. If the wildness he showed in AAA comes back, hitters (especially lefties) are going to eventually figure him out and he's probably going to become a very good reliever. The Brewers, however, need to give him every chance to figure out how to start effectively in the big leagues-- because talent like this doesn't come around all that often.