Residents near the Bourbon Street Bar and Grill began calling police about 11 p.m., reporting that a large crowd was gathering there, Concord police Lt. Andrew Gartner said.
At about the same time, the owner of the bar at 2765 Clayton Road also called police for help dispersing the crowd of about 100 people, who had been turned away after the club reached its maximum capacity of about 250, Gartner said.
A posting about the event on the business's Web site said doors were to open at 8:30 p.m. for a 9:30 p.m. show called "Preppy Sensation Presents THE WINTER PARTY Feat: DJ Truth."
Arriving officers found a half-dozen fights had broken out among the throng outside. When the crowd refused to disperse after repeated orders over loud-speakers, and a few people began charging officers, Concord police put out a call for mutual aid, Gartner said.
Officers from Pleasant Hill, Clayton, Walnut Creek, BART and the Highway Patrol, as well as Contra Costa Sheriff's deputies responded, with a total of about 55 on scene, Gartner said.
"They needed our assistance," CHP spokesman Scott Yox said. "There was a large crowd they were trying to disperse. Once they started breaking up, we started getting reports of sideshows in Concord."
Officers set up a skirmish line to push the crowd away from the club doors, subduing one brawler with a Taser.
Chris San Miguel, who took ownership of Bourbon Street about a week ago, said the hip-hop act had been booked by the previous owner and, unsure of what to expect, he had added personnel and security precautions. When more people showed up than the club could hold, San Miguel ordered the doors closed.
"It was more people than we were expecting," San Miguel said. "We wanted to keep it low-key."
When he received word of the melee, he shut down the event completely.
San Miguel said he does not plan to hold future hip-hop events at the club, which will feature rock'n' roll and comedy acts, and will meet with police about preventing any similar disturbances.
About an hour after the brawl, police reported a sideshow at Clayton Road and Gateway Boulevard, where about three dozen people congregated, Gartner said. When they spotted police, the group dispersed.
About the same time, CHP officers responded to a shooting on Highway 24 in Orinda that investigators believe also may have involved individuals who were at the Concord event, Yox said.
Using information from witnesses, officers stopped an SUV in Oakland. The 19-year-old driver told police he and four passengers were fired on by the passenger of another car as they headed west through Orinda, Yox said.
The gunman stood up in the car's sun roof firing, Yox said. One bullet went through the back of the SUV, grazing the driver in the back. He was treated and later released from Highland Hospital.
The suspect car, described as an old model Mazda RX-7, has not been found.