Here is a link to the Yankees website showing the play.
http://newyork.yankees.mlb.com/media...16587&c_id=nyy
Right-handed batter Alex Rodriguez hit a high fly ball down the left field line. It crossed the home run wall well higher than the top of the foul pole, then hit a stadium wall maybe about 75 feet past the home run wall, and maybe about five or ten feet foul (there is a yellow vertical foul line painted on the stadium wall). A straight line from home to the contact point of course would have been foul, but this ball of course was presumedly hooking. So the third base ump has to make a judgment call about whether the ball was above fair territory when it left the field of play. OBR 7.05(a).
The camera angles were not the best, which would be looking right down the line. Assuming even a soft hook, it is pretty clear that the ball was at least ten feet fair when it passed over the home run wall.
But what if it were closer? What if the ball was within a foot of the foul line when it passed over the fence? Is the calling ump going to think, well, I think it was foul, but I'm going to call fair and let the replay camera make the final call. What if replays are inconclusive? Then the original call would stand. So giving the benefit of the doubt to the home run cannot be correct.