Relative rookie opinion, but here it goes. No book handy, but I believe that intent is not required for interference, right. R2 interfered, so batter is out. I would rule obstruction based on R2's actions leading up to contact. If he was unaware of fielders approach from behind, or was looking at his coach, etc., I rule obstruction and award him 2B, as he wasn't attempting to advance. If he was holding his ground in an attempt to hinder, then it's interference, which didn't matter as catch was made, and he's tagged out after train wreck. But, then again, was it automatically obstruction, due to contact by fielder, impeding his right to a base, without the ball??