Alderson, 20, is a solid starting pitching prospect whose specialty is control. He was the Giants' first-round pick in the 2007 draft, and he made short work of the low minors. He also has a good breaking ball. He doesn't have much of a fastball, though, and may struggle some as he moves up the chain. He's a much better bet than most 20-year-old pitchers to be a fairly productive major league starter, but he probably won't be a superstar, and all 20-year-old pitchers are risky. Alderson is young for Class AA, but the fact that he only posted 46 strikeouts there this year in 72.7 innings is worrisome for a pitcher of his type.
For what it's worth, though, John Sickels rated him a "borderline A-" prospect before the season, which is very good.
I'm excited to have Alderson in the organization, but the chance that the Pirates get nothing from this deal is fairly high, and I'm not sure Alderson's upside--I'd say he's a #3 or borderline #2 starter if all goes well--is worth it. I can certainly see why the Pirates made this move, and I think it's nice to balance the grab bags they got in the Jack Wilson and Nate McLouth trade with a riskier deal for more of a blue-chip player, but I'm not sure Alderson is the right blue-chip player. I really hope he proves me wrong, though.
There's a really good writeup on Alderson here. There might be some hidden upside in this deal if his changeup develops, but then that's true of about a billion pitching prospects. I've never seen Alderson pitch, so I'm open to the idea that this is a good deal, but his strikeout numbers do worry me some.
The key here, I suppose, is that the Pirates weren't going to get much for Sanchez; his option next year will be for close to market value, so there was little reason for any team to give up the farm for him. That the Pirates got a guy a lot of people consider one of the Giants' top prospects is, I guess, to their credit. It's just that Alderson really isn't the sort of prospect that gets me going.
People never seem to talk about this with regard to players who have already been drafted, but if you go to Baseball Prospectus and look at the PECOTA comparables on a bunch of prospects' player pages, what you'll see is that, with blue-chip hitting prospects, most of the top comparables are usually guys who had good major-league careers. Let's take the Blue Jays' Travis Snider, for example--his top comparables before the season included Prince Fielder, Derrek Lee, Cliff Floyd, Eric Chavez, Paul Konerko and a bunch of guys who are still prospects. But if you look at Rick Porcello, a pitching prospect widely considered to be more valuable than Snider, the comparables include Roy Halladay right at the top, and Jon Garland a bit farther down the list, but they also include tons of flameouts--comparables #2, 3 and 4 are Matt Drews, Jamie Arnold and Sean Burnett. If I were the Tigers' GM and I were offered Snider for Porcello, I would probably do that trade, despite how Snider has played this year.
This isn't because PECOTA has some bias against pitchers. It's because pitchers are, by their nature, extremely risky, much riskier than most prospect lists would lead you to believe. This is why it's mostly dumb to pick them early in the draft. The way to get them, in my opinion, is to do exactly what Neal Huntington had done before today--grab high-risk arms late in the draft, and pick up others (such as Jeff Locke, Bryan Morris and the guys in the Jack Wilson trade today) in package deals. Not all of them will work out, so you focus on quantity and upside and don't focus too much on any one of them. Alderson is less risky than most prospects his age, but there's still a strong possibility that he'll have some catastrophic arm injury or lose velocity or struggle with his mechanics or any number of the other weird things that happen to young pitchers.
Is the upside here worth the risk? I'm not sure it is. I'm not sure it isn't, either, but this trade still makes me a little uneasy. I know that every prospect guru is going to say this is a great trade for the Pirates, and I understand why they're going to say it, and I hope they're right. But I'm not really sure most of prospectdom's chattering class really evaluates pitchers properly. That's my humble opinion, at least.