I've seen things like this escalate to violence a number of times when I was on the job. Our instructions were to always try to talk people down from that ledge. Things get out of control way too quickly in one on one situations. This thug is backed by a gang? A bunch of anti-social punks who think an insult or a challenge to one of their crew is a declaration of war? Yeah, advise the civilian to beat his chest...that'll do it.