It is hard enough to tackle in the NFL good luck trying to do it by aiming for one small part of the body.
If my memory serves me correct there was a minor tweak to the rules regarding hair which makes it illegal to grab and pull back ward like a horse collar but that so long as you dont pull the player backwards over over his own legs you are good.
I believe they tried to ban the dreads but were blocked by the PA as players claimed it was a cultural thing and the league had no rights to interfere.