Police were called to Pepperbellys Variety Theatre and Lounge, 849 Texas St., to respond to a shooting around 12:15 a.m., Officer Cleo Mayoral said.
Bay Area comedian Rex Navarrete was scheduled to perform Saturday night.
The shooting was possibly the result of some verbal or physical conflict over a woman, Mayoral said.
The victim, a 29-year-old Vallejo man, was shot once in the abdomen. He was transported by helicopter to a local trauma center, where he was listed in critical condition following surgery.
"It appears he's going to survive this," Mayoral said after checking on the victim's condition at 1 p.m. Sunday.
Police have yet to identify an exact motive and a suspect, Mayoral said, and they are struggling to identify and interview witnesses. "A lot of people left the scene because it was so chaotic," Mayoral said.
After the shooting, various small fights broke out among the remaining patrons.
The raucous crowd refused to disperse and caused disturbances both inside and outside Pepperbellys.
Concerned about the damage the crowd could cause to the businesses storefronts, Fairfield police called the Solano County Sheriff's Department and the Vacaville Police Department to help tame the large, unruly crowd that had become hostile to officers, Mayoral said.
Police sprayed pepper spray into the air to encourage the crowd to disperse, Mayoral said.
No officers were injured. A few patrons were treated for exposure to pepper spray, Mayoral said.
Once reinforcements arrived, authorities were able to control the scene.
Five people were arrested for public intoxication, fighting in public and resisting arrest. The suspects, Bernard Ingram, 41, of Vallejo, Shaina Hamilton, 22, of Sunnyvale, Alyssa Espinoza, 21, of Fairfield, Eliza Smith, 28, of Palo Alto, and 21-year-old Shameka Hamilton of Morgan Hill, were booked into Solano County Jail.
"I'm sure alcohol played a role in the decision a lot of people made," Mayoral said.
Anyone with more information about this incident is encouraged to contact the Fairfield Police Department Major Crimes Unit at (707) 428-7300.