HCT

[JasonTX]

Team A throws a legal forward pass towards A88.  As the ball touches his hands he is contacted by B22 and the ball hits the ground and incomplete.  The contact by B22 was such that it was an abrupt pulldown by the back of the A88's collar.  It had all the earmarks of a horse collar tackle, but can we call it that without A88 being a ball carrier?

[ElvisLives]

The rule is very specific: it only applies to a ball carrier. The rule also goes onto say it applies to a potential passer (but not the passer) inside the tackle box. But, any player in possession of the ball is the ball carrier, so, the part about the ‘potential passer’ is unnecessary.
In your scenario, A88 is not the ball carrier. No foul. (Until it happens to a highly paid QB who gets injured by the tackle.)