Over and back

[Emjaykay]

I have a couple over and back questions that I was hoping someone could answer.

1. If there is a loose ball and an offensive player steps on the half-court line just as he's established possession (the defensive team had the last established possession before the ball was knocked away), is this an over and back violation?

2. Is merely stepping on the half-court line a violation, or does the ball have to pass over the line as well? I had heard once that if 3 points (2 feet and the ball) have passed over into the frontcourt, 2 of the points have to pass back into the backcourt for there to be a violation.