By saying "The defender contacted the quarterback, causing him to fall to the ground. By rule, this is a personal foul." Ed is saying that anytime a defender contacts the QB and the QB falls to the ground, it's a PF. I don't think that is the case so he missued the phrase here.
He should only use "by rule" when an action leaves no judgement at all in deciding what happened,i.e., "The kicking team recovered the ball. By rule, the ball is dead where recovered."
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