Ok, Best way to Contain the Scene....
So you have a small Riot on your hands? "Resist! Resist! Resist!" Is what the crowd is chanting.... You got some idiot running around inspiring people to chant Resist along with him.... Well never Fear.... The City of Los Angeles has the best Units to respond to a call of this magnitude.
Step One: The FIRST Unit on the Scene of a Riot should ALLWAYS Be a SWAT Truck Equipped with a Water Cannon (I know it dosent sound nor Look very realistic for a Tank to be the first vehicle to show up, But If Officer Saftey is your First Priority then you do so)
Step Two: Dispatch 4 Units of LAPD SUV's to the Scene, Get your officers to set up an Outer Perimiter so no other idiot can decided to join them.
Step Three: Make sure you have atleast One LAFD Mass Casualty Unit or 3 EMS Paramedics on Standby.
Ok, so your tanks on the inside Giving people free delousings, That means they should start scattering...
Make sure that out of every Police SUV that you dispatched to the scene earlier 2 Officers are dedicated to Perimeter Containment, All other officers are free to roam the area and try to arrest rioters.
Tip: If you find the first guy who starts the Riot, You have a bigger chance of Shutting down the riot VERY Quickly. (If your tank gets on the scene and There only one or two people standing there then try to arrest them BEFORE other Unruly Citizens arrive. If you get them before hand, Just grab any Crusier in the area and send em down to CJ for DTP and Disorderly Conduct)
Tip: Try to get no more than 3 officers Dedicated to arresting one person... If not, You may have not only the headace of an injured person in the riot zone on your hands, but also a Lawsuit coming for excessive force (But dont worry about the lawsuit, LAPD is used to getting them for calls on excessive force

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Ok, You got officers Rounding up Rioters, But they are still coming and gathering at a point and chanting "Resist" Still? THAT Means you have either a Breach in containment, or theres a walkway that they can acess that you didnt know about. At this point repeat the process of wrangling up and keep your SWAT Tank on the exact position that they gather at to chant resist. That keeps them away from being able to further riot. At this point, YOU should have te upper hand, Stay agresive and wrangle up ANYONE who comes to the scene, at this point, Call in your EMS Vehicles to Evac any wounded (Now that you SHOULD have the area secured)
Call Extra officers in Vehicles to the scene to put these suspects in the back of the cars and send em all back to Dispatch.
Keep your SWAT Truck on the Scene along with a Cruiser of Officers Whilst you send all your other units responding to the call back to HQ, If all units return to HQ and you get your points for a Job well done, Then send the rest back, If not Pay close attention to anyone who is running in the area, They are your prime target (Whoever runs is usualy the guy who ensued the Riot in the first place. Keep your tank on scene and get your Crusier to get after him! Apprehend the suspect and Take him back to CJ, Thats when you get your points and you can recall all Units on Tactical Alert for the Riot back to Base
It's complicated, But works out fine with me.
Theres your little hand book into My Two Cents in Containing a Riot