The incident began shortly before 1:30 a.m. at The Rocks Bar and Lounge at 146 Kentucky St.
Two Petaluma police officers were on patrol in the area when they saw a crowd of about 100 people outside the bar and heard what sounded like Tasers being deployed by the bar's security staff, police said.
According to police, a Sebastopol man named Timothy Traylor, 22, had allegedly been climbing on sound equipment inside the establishment. When security staff attempted to kick him out, he allegedly punched one of them.
When the Petaluma officers showed up, security staff asked them to arrest Traylor for battery, police said.
Traylor, however, allegedly resisted the officers as they attempted to take him into custody, and a friend of his, 22-year-old Healdsburg resident Kathleen Zanoline, allegedly tried to physically intervene in the arrest, police said.
The officers repeatedly told Zanoline to move back, but she refused, police said.
The officers called for all on-duty officers in the city to respond to help control the crowd as more people came out of the bar and began to move toward the officers, police said. Several intoxicated people were allegedly verbally challenging the officers.
Petaluma police also requested assistance from nearby agencies, and a total of 20 officers from the Sonoma County Sheriff's Office, the Cotati Police Department, the Rohnert Park Department of Public Safety, and the California Highway Patrol responded to help.
At one point during the incident, someone tried to approach a Petaluma officer's police dog. Another officer intervened, and the dog bit the officer.
Also during the chaos, a sheriff's deputy was backing up his patrol car slowly with his emergency lights on when someone walked behind the vehicle and was hit.
The person was not seriously hurt, but was transported to a local hospital to be treated for a complaint of pain, police said.
The officers ordered the crowd to disperse south on Kentucky Street toward Western Avenue and formed a line to move people in that direction, police said. Several people had to be physically moved because they allegedly refused to disperse, police said.
It took the officers about an hour to completely disperse the crowd.
Traylor and Zanoline were arrested during the incident.
Traylor was booked into county jail on suspicion of battery, resisting arrest and possession of methamphetamine. According to police, his blood alcohol level was .19 percent.
Zanoline was booked on suspicion of resisting arrest, police said.
Petaluma police have responded to more than 50 calls for service at The Rocks during the past year. Over the past several months, however, the calls have been more frequent and included reports of several fights, a stabbing and a robbery, police said.
In October, police officers met with the owners of the bar and told them they were in violation of the City Business Conditional Use Permit requirements and a local alcohol-related nuisance ordinance.
The owners agreed to remedy the problem, but by early November, the issue still had not been corrected, police said.
On Nov. 24, several fights started in front of the bar.
Officers from the Department of Alcoholic Beverage Control were conducting a plain-clothes operation at the time and cited the bar for six administrative violations, police said.
Petaluma police also cited the bar owners for local ordinance violations.
The Police Department is working with the Department of Alcoholic Beverage Control to investigate the incident today, as well as past incidents, and look into how the business is being operated, police said.