Can someone explain why it is ok to straight-arm a defenders helmet?

[NoCalMike]

I dunno if this has ever been explained before, but I am not sure why RBs are allowed to basically twist and turn a defenders helmet every which way when straight arming their head/face, but the minute a defenders hand grazes a helmet, it is a personal foul. Is there something in the official rules that makes it ok, or what? I mean I see a lot of runs by RBs get extended by 2-3 yards because they basically throw a punch at the defenders helmet, but it is called a straight-arm.

:2cents:

[Barney B]

Well, I think it's been in the rules forever.

As long as the ball carrier doesn't actually grab the helmet, it's perfectly legal, so I'd bet that the defenders could do this too.

But why would a defender stiff-arm a guy who they're trying to tackle? They never would, 'cause they're using their hands to grab the ball carrier in order to tackle him.

Does that make sense?