its because, bella didnt punch paul, she slapped him and really you cant injure yourself by slapping anything, but my punching you can, so quit the question cuz ur wasting everyones time trying to explain why this is,
Well in the book she don actually ever do anythin 2 paul, in the film she kinda just slaps him, wheras jacob she physically punches him in the face full force-causin her 2 like break her hand.
Well it’s because Paul isn’t as strong as Jacob which is shown in their battle Jacob has more strength that being said he is the strongest in the pack which is why it hurt when Bella hit him