Text-book example of the dynamics of a protest: We have a main-stream demonstration, peaceful and then there is a small group with different – more activist tactics – which infiltrates the main protest and by taking the vanguard in confronting the police, they change the entire character of the original demonstration.
Now the police has two choices: Pin-point the response and segregate/control the violent minority or generalize the repression and go about it indiscriminately. In the latter case, the authorities risk radicalizing a segment of the original peaceful demonstration.
That sequence can repeat itself once and again and when enough of the main-stream protesters are radicalized, we have a revolt or a revolution.
Of course the small militant minority hopes that the police will be indiscriminate in its repression of the protest.