I would be among those most thrilled if the Pirates were to acquire Justin Upton. I think that he is an MVP caliber talent and would make the Pirates a force to be reckoned with going forward. That said, there is room for caution.
This is in large part due to the fact that Arizona is so determined to get rid of Upton. Even if Upton caused problems with character issues, major league teams rarely dump players simply because they have character issues. Delmon Young is still in the league, for crying out loud. So why are the Diamondbacks trying to trade him?
If I were thinking about acquiring Upton, I would try to determine this because it is quite possible that the Diamondbacks are worried about his skill set. This would be particularly troubling because the Diamondbacks have more information on Upton than anyone. Evidence suggests that players that switch teams, who often are not wanted by their old team, perform more poorly than those who are retained by their old team.
If the Diamondbacks are worried about Upton’s skill set, then the Pirates should be cautious in evaluating him themselves. I am still of the opinion that if the Diamondbacks trade Upton they will regret it. However, there is evidence that suggests that the trade might not work out for the Pirates.
Note: all of the theoretical work found here was done by other authors, notably Matt Swartz, whose work on the subject can be found in the Hardball Times 2012 Annual, and Jesse Wolfersberger at FanGraphs.