Policy with the company I work for is for the first offence all parties get a written warning. Next time they are fired.
I had a situation a few years back when we were laying cable off Hong Kong. We were back in port taking on provisions and the crew were going ashore after work at the end of each day. A couple of them got into a disagreement which they unfortunately brought back to the ship.
I got called to one of the crew cabins late that particular evening because of a fight. Bearing in mind all of them were on a warning already because of an earlier scuffle. This time one guy punched up another (again) so I sacked both and signed them off immediately. The agent came on board at midnight and sent both to separate hotels. Personally I will not tolerate fighting between the crew as it always developes into a worse situation later on and once at sea it becomes a nightmare to get them off and home.