he was brave and - probably stupid. he calculated that the other guy - probably drunk? - will not attack him, does not have a knife, etc. he risked giving his child an experience much more traumatic and unpredictable than listening to dirty words.

moreover, he was practicing vigilantism and threatening battery. which would be excusable in self-defence, but in most courts even verbal assault is considered a weak reason for a physical scuffle. what he should have done this father, is change carriages. or try to distract the child somehow. and not to engage a sociopathic and possibly dangerous creep.