I've seen so many bowl games, I forget in which it happened, but yesterday was a good example of a blown call on the "runner down" question. I commented on it at the time. The ball-carrier was running along the sideline. The first defender tried to block him out of bounds. Instead, the runner simply ducked his shoulder and rolled up and over the back of the defender in one smooth motion, never stopping his forward progress and no part of his body having touched the ground. He got about one more step when the second defender hit him with two hands, knocking him OOB. Result? The linesman drops the flag and calls the second defender for a PF. If there were a whistle, it was much too quick, because, as said, the runner never touched the ground or stopped...
Good example.
Still another example from yesterday (don't recall which game): the defender tackled the runner by grabbing his body and both fell to the ground in a rolling motion. The defender hit the ground on his back and the runner landed on his back on top of the defender. No part of the runner touched the ground. In one smooth rolling motion, the runner rolled off the defender with only his feet and hands touching the ground. The runner continued running... but the official blew the whistle. So should the whistle have been blown?
In this situation, since the whistle was blown, if another defender had de-cleated the runner after he jumped up and started running again (but before the whistle blew), he would very likely have been hit with a flag. But if the whistle hadn't blown, this same defender would have watched in disbelief as the runner jumped up and ran for a TD. After being on his back on top of a defender.
Under what I assume are the present rules, too much judgment is required of a defender when a runner is tackled but rolls over the body of a defender and maybe-he-did/maybe-he-didn't touch his elbow/knee to the ground. Defender must make a split-second decision whether to "re-tackle" the runner and risk a penalty or stand back and watch the runner keep going.
The solution is not to keep playing until the whistle blows. That'll result in way too many roughing flags. IMO the solution is to change the rule to when a defender is laying on the ground, the defender becomes an extension of the ground.
And no, if this were the rule, I wouldn't complain if Ingram were ruled down in a similar situation.