Where is Dangerous Waldo?

A massive demonstration in support of reformist candidate Mir Hossein Mousavi is formed as supporters gather on the streets of Tehran to demonstrate against the results of the Iranian presidential election, in Tehran, Iran on June 15, 2009. The march came hours after Iran's supreme leader Ayatollah Ali Khamenei ordered an examination into election fraud.

There are several things you could look for if you were in charge of security and evaluating who is most likely to erupt in violence.

This situation is tenuous at best, and as we later learn violence did indeed breakout. Crowd hysteria and/or mob violence is the most serious and dangerous of situations and once a crowd become violent it often leads to the most serious of man versus man assaults; where whatever had brought them together is soon forgotten and the strong pounce on the weak regardless of ideology or sides. It becomes an opportunity to inflict pain on another human simply because the adrenaline is present and the opportunity has presented itself.

I see one person who is a threat. I have placed an explanation in the comments, and I will outline what to look for...