While I think that was interference, that same type of contact has gone uncalled several times this year (Lowell and A-Rod's slides come to mind). I'm surprised that the call was made.

I think the fact that Upton barely even tried to touch the base had something to do with the call. Plus, with where his body ended up, it looked like he was rounding second base and trying to slide all the way in to third base. I haven't seen the slides referred to in the previous comment, but I would have called this interference even with out the forearm. If Kaz hadn't moved his back foot, I'm pretty sure it would have been broken by Upton's slide. It looked like Upton was aiming for it.

why did the runner have to go back to second? seems like he would have been at third regardless of the interference.

Stupid slide, it was crystal clear he was under the magnifying glass after the words. Good call, play ball.

Joe Sheehan had a great take on the slide today.

"Vanover is correct--Upton was trying to use his body to make sure that Matsui couldn't complete the double play...which is the intent of just about every runner going into second base every day in every baseball game. The difference here is that Upton was successful with what looked to me like an aggressive, but not dirty, slide. We--and players in today's game--have to hear all the time about the way Hal McRae and guys like him went into second base. Then a player actually executes that play, and he gets nailed for interference. Meanwhile, catchers can block home plate, trip runners, and set up five feet up the third-base line without the ball, and obstruction is never called.

Last night's play was on the margin between legal and interference, and I don't think you can fault Vanover for his call. However, in the context of how plays around that bag get made, with runners routinely going six feet to the outside of the bag to try and take out a pivot man, it seems a little ridiculous to me to make a stand on this particular point. It goes back to a point we've seen made many times over the past few weeks: there are rules on the books that are enforced arbitrarily, and when that is the case, you have inconsistency and the potential for controversy. By the rule book, Vanover made the correct call under the rules, but games are no longer umpired by the rule book, but by a de facto set of standards developed over generations. That, and not a specific call by a specific umpire, is the problem."