At about 10:30 p.m., officers were patrolling a "Mac Dre Day" event where 1,000 to 1,500 people were gathered at the North Vallejo Park near Whitney Avenue and De Paul Drive, Vallejo police Sgt. Jeff Bassett said.
Officers heard gunfire shortly before they spotted a man with a gun fleeing the park, Bassett said.
The officers gave chase and then shot the man multiple times, although it is unclear at this time whether the victim shot at the officers, he said.
Police are asking witnesses and others with information to contact the department at (707) 651-7146.
Mac Dre is the stage name of Vallejo-raised rapper Andrew Hicks, who was shot and killed in Kansas City, Kan. in 2004. Saturday's event was a celebration of the rapper's upcoming July 5 birthday - he would have turned 40 on Monday.