I have had the pleasent experience of being caught in 2 situations of urban unrest.
The first time I was walking up an alley way in London minding my own business, looking at a book, i was oblivious to what was going on around me until it was too late, I was standing in the middle of the street alone, to the right of me was a hord of English soccer fans being held back by police, to the left of me was the Brazilian soccor fans also being held back by police, I stood there for a moment wonder how in the hell I ended up in this situation, then it hit me! Well not hit but wizzed by my head, a frik'n pint glass smashed on the ground beside me..one of the police officers started to scream at me to get out of the "hot zone", needless to say I took off pretty quick..I found out later that the world cup of soccer ( or something like that) was going on.
The second time was in Melborne Australia, I was watching a Anti-Globalisation protest, it was pretty peacful at first, songs and sloggans and you know the regular thing, then in a secaond all hell broke loose, some of the protestors had started up with the police, and what came next was pretty bad, mor ecops than I could count against even more protestors...holy crap!!!! I took a bit of pepper spray in that incident, but I got out of the melee in tacked.
The moral of these stories is, if you don't want to get involved, then don't be there, beacause it can go bad in seconds!!!!