I still don't think it's such a big deal, but it does look like A-Rod was possibly trying to rattle Braden and get under his skin--something I have no problem with.
Either way, I've seen a disturbing trend over the last 12 hours or so, and it's Yankees fans throwing A-Rod under the bus for this. First of all, who cares? Do you as a Yankees fan really give a damn about Dallas Braden's feelings? I know I don't. If he's got such a problem with what Alex did, let him put one between A-Rod's numbers the next time they face each other. I also have to imagine if Jeter did something like this, even if it was an accident, you wouldn't hear a peep from the same folks who are now calling A-Rod things like a bush leaguer.
(Updated) The guys over at Fack Youk have a nice collection of quotes regarding the subject that you should check out.
There was one from a BBTF commenter, who said that a buddy of his who pitched in the minors said that he would have reacted the same way Braden did. And also said "he wouldn't have thought any player in the majors would even consider running across the mound, knowing how pitchers would react."
For more on this topic, check out this post over on The Baseball Codes. Jason Turbow, who wrote a book about this stuff, talks about the rule. He mentions that it is something that players know, but there are guys likes A.J. Pierzynski, who make a habit of doing this to piss pitchers off.
Based on all of this A-Rod had to have known the rule and clearly did this on purpose to try and rattle Braden. My only complaint is that it didn't work.