If you're going to let them go, let them go. Don't hold one player back so he has to eat punches to the face without having the chance to protect himself. There was a situation just like this in last night's game between the LA Kings and Minnesota Wild.
This game got heated in the third period while the Kings were leading 6-0 as both are fighting to keep their playoff hopes alive. The Wild's Ryan Hartman and LA's Pierre-Luc Dubois were exchanging words when tempers boiled over and Hartman dropped his gloves. Dubois clearly didn't want any part of it (his team was leading 6-0 after all), and tried to get away from Hartman before taking any damage. However, a linesman who must have thought he was trying to break up a fight, help on to Dubois while Hartman delivered multiple punches. Dubois was given no opportunity whatsoever to protect himself. This, if course, brought in several other players to get involved.