Runners will have to keep their heads up and not drive their helmets into defensive opponents, lest they get the yellow flag and accompanying penalty. It seems most players appear to be against the rule and feel they will either have to re-learn how to run or hope the officials do not constantly enforce the rule.

The problem that will occur will be the officials interpretation of it and there are sure to be crucial points in the game when a play is flagged and a huge gain or key first down will end up being negated by a penalty.

Take this scenario, for example. Third and goal from the opponent's five yard line in a close game. Baltimore Ravens QB Joe Flacco drops back to pass and lobs a swing pass to RB Ray Rice in the flat. Rice heads for the end zone where two defenders come up to prevent him from crossing the goal line.

Rice lowers his heads and bulls into the end zone for the touchdown and an apparent Ravens lead late in the game. But hold on there, fans, a referee has thrown his yellow hankie and the officials are huddling in the end zone. Penalty on Ray Rice, for lowering his head into the defender. Touchdown negated, 15 yard penalty and the game is now changed.

How will this rule be enforced, what are the coach's abilities to challenge a call like this (none), and how many calls will result in having a significant effect on the outcome?

Check out the related SB Nation story on this and the other rule changes that were just approved at the NFL Owners Meetings.