Last December, James Shields was traded from the Tampa Bay Rays to the Kansas City Royals, for four prospects. But, according to Ken Rosenthal, Shield nearly became a Diamondback instead:

"[KC GM Dayton] Moore didn’t know it at the time, but he nearly lost the deal that night... to the Arizona Diamondbacks. As Moore huddled with his advisers, three other GMs — the Rays’ Andrew Friedman, Diamondbacks’ Kevin Towers and Texas Rangers’ Jon Daniels — were deeply engaged in their own trade discussions. Those discussions, according to major league sources, centered around a three-team deal that would have sent Shields and [pitching prospect Wade] Davis to Arizona, outfielder Justin Upton to Texas and a package of prospects to the Rays."

It's not clear how or at who's demand the trade failed to be consummated - though the article notes that the following day, the Diamondbacks signed free-agent Brandon McCarthy, which may well have reduced their interest in Shields. Would that have been a better deal than what Arizona got for Upton in the end? Hard to say, not least because Shields remains a free-agent after 2014 [it's not clear how hard the Royals have tried to sign him to any extension]. Three years of Upton for two of Shields seems light - though Davis still has potential, even if his star has dropped since being ranked the #34 prospect in all baseball after the 2009 season.