I guess anything is justified in self defense if you can prove your life was in some sort of danger
a kick in the groin is acceptable in other non-life threatening self defense situations too (to protect her stuff for example). On the other hand, most times a man is threatening a woman it is a life threatening situation for size/strength reasons.
Only as a last resort if the man doesn’t stop after verbal warnings and had no reasonable option to disengage from the situation(like some sort of argument gone wrong)