I can't even imagine the unholy beatdown that will befall the first "anarchist" that they see aiming his slingshot at a police horse. There will not be an inch of skin left on their body without a purple nightstick welt.
The police know who will be messing with them, but I'm not sure the trustafarians are as informed as to the nature of their enemy.
Just call out the NY National Guard and handle it like they did the Draft Riots in 1863 if anyone gets violent: mostly infantry and cavalry, but also light artillery firing canister down the Avenues.