[MD Longhorn]

Well, consider all of the following:

1) for a batter to be out for contacting the ball while outside the box, the entire foot must be entirely outside the batters box AND contacting the ground at the moment the pitch is struck.
2) the batters box extends toward the pitcher considerably farther than most people think.
3) MOST of the time, by the 3rd batter, that box is gone, at least the top line.
4) when a pitch is coming in, what is PU looking at? Hopefully the ball itself.

So ... PU's job is to watch the ball as it comes in, so is looking at the ball. To call an out, you must see the foot, the ground, and know exactly where that box is, all while looking at the ball and not the foot or the ground.

I think you can probably see where this is going.

I'm not saying this should NEVER be called. But what I am saying is that being sure of EVERY thing you are supposed to be sure of to make this an out only happens in the rarest of occasions. And I would bet that of all the times I've called it - more than 75% came when batter began a slap, pitcher threw a change, and the batter still hit the ball - usually after falling WAY forward on a pitch I had likely stopped tracking due to it being an obvious ball.

On a normal pitch, it's very very difficult to be absolutely sure of ALL of the things you need to have for there to be an out.