So if you have incidents happen all over during a protest, how many cops do you need to settle it down. In a crowd of thousands how much is to much or to little. Who determines that once things jump off and how long does it take to know the situation. Everything is happening in real time and communication is complex during these events. Either way, I see your point but I am not sure if we are arguing the same issue.
The police aren't just sending out random numbers of officers. They have a general idea of what should be needed, and react to that depending on how the incident plays out and whether the officers feel they need more support. While a dramatic increase in violence over an extremely short period of time isn't something you can do all that much about on the spot, it's not often for things to get out of hand that quickly. As tensions rise, more support should be called for and should be on hand to be sent. Sometimes the officers on site don't read the situation very well, or sometimes the police on site are left in a tough spot as they are told to basically stand down by a higher authority.
I'm not trying to say the police should be perfect, and I'm not saying it's completely their fault and no one else is to blame, but based on the fact that the point was focusing on police, they can certainly better handle their portion of the situation. That isn't the only problem though, and so it would take more than just better policing to completely solve the issue.
Want to know why God gave people five fingers? Because there's always more than just one entity to blame.
The Canadian National Anthem According To Justin Trudeau