Jose Tabata is a warning for sellers at the trade deadline

Jose Tabata was supposed to grow up to be something special when he was acquired by the Pirates in 2008 for Damaso Marte and Xavier Nady. The Pirates were supposed to be getting a building block and potential franchise player to pair with Andrew McCutchen, who was still working his way through the minors, for the next decade. But as the Pirates designated Tabata for assignment last night, and as we approach the trade deadline for 2015, we should absolutely question just how much a prospect is worth, and whether we may be overvaluing them.

Tabata was one of the top 30 prospects in baseball when he was traded. Just 19 years old, he had struggled against Double-A pitching in Trenton for the Yankees. Still, he had not embarrassed himself, and given that he was one of the youngest players in the Eastern League, there was an expectation that his performance would catch up with his talent after some additional experience.

And for a while, it looked like that was actually happening. Repeating the level in 2009, he hit .303 with a .370 OBP and even had a .744 OPS in Triple-A. He was on the verge of the Major Leagues, and he debuted in 2010 at just 21 years old. In 2011, Tabata signed a contract extension for up to six years that provided the Pirates with some cost certainty at relatively little risk.

Everyone was happy and there was every expectation that Tabata would continue to develop. But he didn't. He stalled and fell out of the Pirates' plans. Now almost 27, he never developed any power and has been a liability on defense in the outfield corners. In parts of six seasons, he has been little better than replacement level.

What specifically went wrong with Tabata isn't the issue; what is is the notion of risk. We often treat these trades and contract extensions as if they are de facto wins for the teams that pick up and retain young players. As Tabata, and the Twins' Alex Meyer, and the Phillies' Tommy Joseph demonstrate, the road to effectiveness is still a long one, even for position prospects. A certain percentage of prospects are always going to fail.

The point is that it's exceptionally easy to argue that teams should trade their veteran excess and bring in young players. But clubs, while far more knowledgeable than fans, still have imperfect information about the players in other systems, and should be wary of highly ranked prospects that a buyer is willing to include. Sellers also need to consider the value they're likely to get out of their veterans going forward, players about whom they have much more information and who are much easier to project.

Playing General Manager on the Internet is fun, of course. I do it as much as you do. But as we do it, we need to resist the temptation to assume that every prospect will hit whatever their ceiling is. By their nature, prospects are still developing and much is still in flux. It's why I don't blame the Phillies for being especially cautious about trading Cole Hamels, for instance, whose contract isn't a liability and whose future production may equal or exceed whatever return Ruben Amaro might get for him. After all, Jose Tabata looked like a sure thing. And look at how well that has turned out.