I probably shouldn't be stirring somebody else's pot, but, from what I've read here, it sounds like NF and NCAA are the same on this subject, although, in NCAA, the word "force" is never used. Nonetheless, all of the principles seem to apply for both sets of rules.
Which brings me to a point.
Somebody made the statement that impetus "...only comes into play if we are dealing with a safety or a touchback, not a touchdown." While pragmatic, that statement is incorrect. Any time - ANY TIME - the ball is dead behind a goal line, the result is totally dependent upon who is responsible for the ball being behind that goal line, and who is in team possession when it becomes dead.
If the defending team is responsible, and the defending team is in possession - there's your safety. If the defending team is responsible and the attacking team is in possession, there's your touchdown.
If the attacking team is responsible, and the defending team is in possession, there's your touchback. If the attacking team is responsible, and the attacking team is in possession, there's your touchdown.
Impetus applies any time the ball becomes dead behind a goal line.
Another point. It also sounds like NF and NCAA are the same with respect to kicking a ball. If that is the case, then there is no such thing as "accidentally kicking" a ball. If the act of kicking a ball is intentional, then that is, in fact, a kick. If a player's leg unintentionally contacts a loose ball, that is not a kick. It is nothing more than the ball being deflected by, or off of, a player, and is just a muff. The words "accidentally" and "unintentionally" should never be used with words "kicked" or "kicks" when discussing football rules. The ball is either kicked (which means one thing), or it is muffed (which means something entirely different). When describing such unintentional action, use language like, "While attempting to recover the loose ball, the ball deflects off of B55's leg." Or, "While attempting to block B33, the loose ball bounces and deflects off of A66's leg." That removes any ambiguity.
Robert