Well, if you saw the game with the Jays on Wednesday you would have seen why. If things aren't going his way then he acts like a petulent child stomping his feet and screaming until someone caves.
For those of you who don't know what happened, basically the Yankees were up by two in the top of the ninth with two outs when Posada launched a pop up to third base. Newly promoted Howie Clark parked under it to end the inning and leave the Jays an unlikely chance at making a comeback against Mo Rivera. However, A-Rod wasn't satisfied with that and obviously thought that Rivera isn't quite good enough because he felt the need to call, "Mine" as he rounded third and Clark, thinking his shortstop McDonald had called him off, stepped aside and let the ball drop.
Now as much as some of us dislike the Yankees, you do respect them as throughout their history they have won games by simply playing the game the way its supposed to be played and backing their talent. There is no way you can respect such Sandlot League styled antics. Rodriguez even mentioned how it was like how Hill had stolen home earlier in the series saying both were extreme acts because they were 'desperate to win'. Newsflash Alex, you WERE winning already.
Jon Gibbons summed it up well, "One thing you know about the Yankees, one of the reasons they're so respected, is they do things right," Gibbons said. "They always have. They have a lot of pride and a lot of class. They play the game hard. That's not Yankee pride right there. That's not the way they play. I thought it was bush league."