This is on behalf of a friend (really!), so it is only her pov and I don't know how much she has added/left out. I wasn't at the event, so can't add any objective information.
She and her exh still live in the same house, as they can't sell it. Last night she went out with a group of friends to her local, and her ex was in the other bar with his OW (not implicated in the divorce) and her parents. Foolishly, friend approached the ex and his party and a slanging match ensued, during which the OW's mother threw a glass of water over friend. Friend remonstrated and OW hit friend twice in the face. At this point the ex and the publican intervened and friend left.
There is a history of DV with the ex (and on one occasion, the friend) being arrested a few times and detained overnight. Because of the previous problems friend does not want to involve the police, she is worried about escalating the situation. Her ex stayed away last night, not unusually, but she is now concerned about how he will behave when he returns home.
I really don't know how to help her. We live too far away to help. I feel she needs to call the DV unit but I understand her hesitation. Any advice would be welcome.