If you are not following the feeds of the people organizing the unrest, it may come as a surprise and you may not have the opportunity to depart. Avoidance would be best, but if you can't avoid, stay low and do not attract attention. Do not be an inviting target of opportunity. Crowds do not behave like rational and logical people. Yes there is almost always someone instigating or even directing, but the majority of the people are like cattle, angry and violent cows. They will follow the leaders. Especially when they believe they will remain anonymous. Anonymity changes the way people behave. A large crowd provides anonymity by itself, but when they are hiding their faces be ready for violence. Know what your priorities are for security (family, self, property), and find an escape route if you are targeted. The first thing a sniper does before he establishes a shooting position is to plan his escape route. If you are hunkering down, know how to get out and away from the threat.