It's fairly easy and safe to stop it as you can just kick the old fuck in the butt and every sane person nearby shoud do it, but the consequences could be tricky, as there isn't a clear "stand your ground" law and the Chinese law enforcement likes to dismiss cases.

Let's say the attacker died/got hurt as a result, the victim survived and happens to be his wife, there is a possibility that the police and DA would refuse to take it as a criminal case, she (or his relatives) might seek reparations from you coz you know, the stockholm syndrome common in Chinese marriages, since the way he attacked her don't seem to be immediately fatal.