I have unfortunately seen this flag come out far too often when the ball carrier was not pulled down to the ground. This is incorrect. For it to be a foul, as Al pointed out by citing the rule, the runner MUST be pulled all the way to the ground. In addition, the primary cause of the ball carrier going to the ground must be the grab itself. If a player has a grip of the inside back or side collar of the jersey, but the primary act taking the runner to the ground is a tackle about the waist, then it is also no foul. A key indicator is the buckling of the runner's knees. If you don't see that, it likely isn't a horsecollar foul. Even if you do see the knees buckle, however, if the runner stays upright or breaks free and then falls, it is still NO FOUL.
*Edit* this post was made when the thread was still in the NFHS topic.