Quotes from the news wire:
The call was the fact that he interfered with Gurriel trying to catch the ball. If you notice, the glove came off his hand. That's when Sam Holbrook called him out for, basically, interference, they made the right call at first, and that it (could not be protested) because it's a judgment call. I understand the passion.
Determining where to draw the line between an illegal slide and a legitimate hard play is an extremely difficult call for our umpires, we have been in discussions with the Players Association throughout the year regarding potential rule changes to better protect middle infielders, and we intend to continue those discussions this offseason.