I have watched hundreds upon hundreds upon hundreds of baseball games. I have seen guys try to slide into first base to avoid a tag and make it. I've seen guys run out of the baseline to avoid a tag and get called out. I've seen guys hookslide into second to avoid a tag and make it. I've seen guys plow over the catcher and knock the ball loose, or not. But this is the first time I have EVER seen a player slap at a player's glove to knock the ball out of his hand. Probably because it's illegal and every player knows it.
I don't necessarily fault A-Rod for doing it. He was going to be out and he didn't want to be out. But it wasn't like there was no penalty for doing what he did. He cost his team ninety feet (Jeter had to go back to first). If he gets tagged out or called out for running out of the baseline, the Yankees still have a guy in scoring position.
Also, I agree, A-Rod was classless for whining as long he did, although I see the point of people who argue that he was just trying to get on base any way he could. After all, I'm still waiting for Frank Pulli to call Reggie Jackson out for interference in the 1978 World Series. Reggie and the Yankees got away with that one, and it was a turning point in the game. (I'm also waiting for the NHL to take away Brett Hull's goal, incidentally.) It was perfectly reasonable for A-Rod to think he too could break the rules and not get caught. But he did get caught, and he should have just walked off the field because he knew he was wrong.