To be clear, the rule regarding grasping and twisting/turning/pulling an opponent’s facemask applies to ALL players. The ball carrier is not exempt.
There is a rule that prohibits all players from continuously contacting an opponent’s face, neck, or helmet - including the facemask, with the exception of a ball carrier. The BC is allowed to ward off an opponents with his hand with continuous contact to the head/neck/helmet/facemask. He can’t strike a blow, but he can ‘ward off’ (commonly referred as a ‘stiff-arm) an opponent. But, in doing so, he can’t grasp the mask, chin strap, ear opening, face opening, or neck opening, and twist/turn/pull the helmet.