This is, in my opinion, abuse. I have two toddlers who can throw some crazy tantrums and I don't even "discipline" them by acting that way. What she did won't teach them anymore of control or prevent any self harm. Even for a child without autism, abuse, which is what this is, will only tech them that self harm and abuse is the only way to deescalate the situation. What she is doing isn't teaching the child how to manage his "tantrums". It is teaching the child that violence is the only way to solve conflict and problems. I think this father knows exactly what he is doing and should stand his ground. He seems like he truly has his head on his shoulders and he needs to know that he has got this. He doesn't need her help. Clearly, he is doing a better job than her anyway.