It sounds counter-intuitive, and will never happen, but if the NFL reverts back to a leather style helmet it would naturally influence players to play/tackle differently. You can't lead with your head when it's not protected. Players in all levels of football would have to revert back to the "form" tackle.
The same can be said for hockey- they should bring back the clutching and the grabbing too.
And I agree with my French soccer rival (a few comments down). Change football's name. Soccer is the REAL FOOTball. ;)
In the beginning of a change the patriot is a scarce man, and brave, and hated and scorned. When his cause succeeds, the timid join him, for then it costs nothing to be a patriot.