I'm a big fan of the stiff arm in football. It's a legal play, it can free the ball carrier and help him break off a long TD. I do know people who think it's BS and that it shouldn't be allowed. I can see some validity to that argument. No one is allowed to put their hands to the face of an opponent, and guys get called for it all the time. Unless they're carrying the ball, then they can unload on a guy.
I have seen offensive players get called for unnecessary roughness on a stiff arm for either grabbing the face mask or just straight out punching a guy with a closed fist. Neither of those are cool, and I can't get behind that. A good stiff arm should be done with an open hand. Delivered correctly, there really isn't any reason a guy with the ball shouldn't be allowed to defend himself from tacklers. Check the gallery for a breakdown of the techniques of these guys.