[Video Link.] Video analysis by blogger Matt Kresling: "Footage from the Occupy Oakland protest, October 25th, 2011. After protesters ran to the aid of a badly-injured person, Oakland Police deliberately lobbed a flash grenade into the crowd. Whatever you think of the Occupy movement, police behavior of this kind is criminal and should be prosecuted."
The Guardian and the New York Times have related coverage.
I'm told that the protester injured in this video was Scott Olsen, a US military veteran in Veterans For Peace. Video which shows him after the attack is here. He is reported to be in intensive care, with serious head injuries.
Update: From Veterans For Peace:
Veteran For Peace member Scott Olsen, a Marine Corps veteran twice deployed to Iraq, is in hospital now in stable but serious condition with a fractured skull, struck by a police projectile fired into a crowd in downtown Oakland, California in the early morning hours of today.
It's important to note that police from many districts throughout the Bay Area and Northern California were involved, not just Oakland PD. But thanks, police at Occupy Oakland—whoever you are!—for finding a unique way to thank American combat veterans for their service to our country.