It is never acceptable to hit a woman.
Kevin and Missy are having a heated argument and Missy smacks Kevin.
Kevin wants to react to Missy.
Kevin is angry he was slapped, so he leaves the house.
Kevin is angry he was slapped, so he slaps Missy back.
Missy and Kevin are both able to calm down and when Kevin returns they discuss things in a civil manner.
Missy falls to the ground from Kevin's force, and she calls the police who arrest him.