[greymule]

My conclusion is that stepping with one foot completely out of the batter's box is out of the batter's box; no matter what rule you reference.

I think that's the correct reading of the rule. In the real world, however, it's more "ball hits batter" is foul, and "batter hits ball" is an out.

For example, if a bunt hits the plate and bounces straight up, and then the BR runs into the ball or her first step toward 1B, that's virtually always called foul. Of course, it's usually hard to tell exactly where the foot was when the ball hit the BR, so a call of foul usually gets no argument.

But if the bunt rolls in front of the plate and the BR steps on it with her foot completely out of the box, that's an out.

Confusion also arises when the ball bounces up and hits the bat or the BR over fair territory, but the batter's feet are both in the box. Foul ball.