While police kept a watchful eye on the protesters, thousands of first responders from as far away as South Korea gathered for the seventh annual Urban Shield conference sponsored by the Alameda County Sheriff's Department.
"What we have here is Urban Shield, which is the largest exercise for police fire and medical in the nation," sheriff's department spokesperson JD Nelson said.
But demonstrators say the event promotes the militarization of police and brutality against citizens.
The law enforcement convention and the protest are occurring on the second anniversary of the police raid at the Occupy Oakland encampment that was erected in 2011.
Scott Olsen, a war veteran who was seriously injured when he was hit in the head by a police projectile during the raid on Oct. 25, 2011, said he's disturbed by what he believes is a trend by law enforcement officials to "paint the public as the enemy."
Olsen said the militarization of police "won't stop unless it is stopped."
Bay City News contributed to this report.