First, a large number of protesters are not farmers. They are pajd protesters from Shaheen Bagh, INC, CPI, AAP, Akali Dal, Khalistani separatists etc.

Second, you need to learn how these "peaceful protests" work and turn ugly. This can be broken down into the following steps:

The opposition and antisocial elements gather some people for the job. A lot of these people are physically strong, trained guys. They have adequate preparation to fight and spread riots, but it is concealed well. The route and everything is planned in advance.

The groups are formed and they start moving "peacefully" for a while, making their presence noted. Many people, who are genuinely affected or are naïve or easily swayed or even just curious, are drawn to the crowd. The numbers start swelling.

Here's when the trouble starts. When the crowd has become big enough, some people from the starting crowd or some of their friends who are not in the crowd will start provoking people. It can happen in many different ways, sometimes they try to pit people from different groups together and sometimes they try to provoke the police.

Provocations keep occurring until things escalate and heat up. And then shit happens. Police just can't keep their hands tied. They try to control but even they are attacked and provoked further. When they start acting in self defense, the assault on them intensifies and then the protesters start playing victim card.

Riots and looting are often done in this stage by taking advantage of the heated situation. While some people in the crowd ARE innocent, they can't be separated from the crowd.

Now the police appears bad and the administration is made to look incapable. But actually everything is a planned, pre calculated game.