So we were gigging the other night and I heard the bass drop out and then a big crash as the bass guitar was dropped/slammed to the floor. I looked in the bass guitar direction and saw our bass player (in the band that I play guitar in) heading into the audience to confront a guy who was talking to his girl. Luckily an actual fight did not break out but it was dicey there for a couple of minutes. To me this was the ultimate in unprofessionalism, and is something that I have never encountered. How should the band handle this?