It could be like normal fighting, but instead of the person getting hurt they get knocked out.
Mugging and mobbing are pretty up close personal knock-em-down-and-senseless kind of activities, so there would be a different kind of damaging system, where heavier things do more knockout damage than "real" weapons. Also I think it would be resonable to assume that whilst mobbing/mugging someone the people/person doing it is doing everything they can to knock the person down and knock em out, so the more people doing it the more advantage they get, basically bundling on top of the target in a big mass.
But perhaps to be successful you need a lot of people, or a minimum. Like dragging doesn't happen until you have enough poeple, mugging doesn't start until you have the minimum, say of 5+.
Just a starter idea, add as you wish
