Flash bang grenade

Oakland Police Tally 39 Arrests In May Day ProtestsLarge protests in Oakland on Tuesday to mark May Day were mostly peaceful but 39 people were arrested, city of Oakland officials said Wednesday.
Occupy Oakland Protest Turns Violent; Hundreds ArrestedPolice arrested around 200 Occupy Oakland protesters during a day of action Saturday that began with the protesters' attempt to take over a vacant building to establish a community center there.