Do you think if the rule 9-2-3d read this way it would be better understood.
Defensive players may ward off or legally block an eligible pass receiver until that
player occupies the same yard line as the defender or until the opponent
could not possibly block him. Continuous contact is illegal.
I really like the phrase "until the opponent could not possibly block him." Think about the play where B runs through A2 to get to A1. Or, when eligible A turns back toward the line of scrimmage.
Oh, BTW. From the NCAA Rule Book.