Americans are occupying more than Wall Street, and some cops are clamping down way harder than those in Manhattan. In Oakland, riot police attacked with tear gas, rubber bullets, and, most vividly—flash bangs. Meet the M84 stun grenade.
The M84 is the Army's friend. You've probably played with a virtual one in games like Call of Duty before kicking down a door and shooting everyone. They're perfect for temporarily blinding and deafening anyone close by, leaving them vulnerable to, well, anything. Each 2/3 pound grenade is stuffed with an pyrotechnic metal-oxidant mix of magnesium and ammonium that creates a thunderous boom (about as powerful as a jet engine) and bright flash (equivalent to that of a spotlight). Think of it as someone shining a flashlight in your face and yelling in your ear. Only much worse. And that's why riot cops love them—a crowd, disoriented as hell by a grenade, is a lot easier to disperse and cuff.
However, there are rules governing the use of weapons like the M84—or at least there are supposed to be. In Oakland, straight from their official Crowd Management/ Crowd Control Policy document, cops can't just go around chucking flash bangs willy nilly:
The use of sound and light diversionary/distraction devices presents a risk of permanent loss of hearing or serious bodily injury from shrapnel. Said devices shall be deployed to explode at a safe distance from the crowd to minimize the risk of personal injury and while moving the crowd in the direction that will accomplish the policing objective