It's all about how you want to play the game. You can use several of my tips and combine them. In my opinion you need to strike as fast as you can before you let the riot get out of control. You can use flashbangs to stun crown members and slowly detain them all. If the mod has a water truck you can use that but keep in mind that will injury citizens.

Tip 4: If the riot is out of control wait for SWAT. I will also dispatch other patrol units but they usually arrive later. Tip 3: I send my nearest patrol car to immediately arrest the man with the sign. Then place 'sign guy' into a patrol car while halting the rioters. Have two officers detain the sign guy and the other two using the halt citizen command. For example, send a group of about 4 officers. Implementing Tip 1 with this is a good idea. Once you place the man with the sign in the back of the patrol car the riot will end. You can also use the 'Halt citizen' command on officers to break them up. This can get the protesters to back up from your officers splitting the massive group. Tip 1: A good strategy is utilizing the K-9 in some mods.

From my time playing EM4 and 911 First Responders I have several tips.