What about the harassing/intimidating people in their cars? About twenty to thirty must have been involved there. Surrounding cars and shouting at people, climbing on them, and some hitting/kicking the vehicles. I know people will say 'oh, they didn't mean any harm' or 'they were just having a laugh';, but I guarantee your perspective would change if it was you in the car. How do you know what a big group of people around your car will do? It is threatening behaviour.
Also, why do people always treat the firing of flares and fireworks so lightly. They can cause horrific injuries if they hit someone. The fact that people are willing to fire them off in public places puts people at risk. There were several fired through the protest. I will never condone their use.
So, it wasn't just one person. There were quite a lot of trouble makers there. And yes, the organisers do take some responsibility for this type of behaviour. When you set up something like this, you know there is a big chance that stuff like this can happen. Let's put things into perspective: is the risk of violence worth protesting what is a game? The answer to me is no.