Police on patrol in San Diego's Gaslamp District at about 2:10 a.m. Monday encountered a three-man fight that included Carrillo in the 500 block of Fourth Avenue, Lt. Andra Brown said.
Carrillo, 31, arrested and booked into jail on suspicion of felony battery causing serious bodily injury and fighting in a public place, according to the according to the San Diego County Sheriff's Department.
He posted bail and was released at 11:42 a.m. that day.
A second man was also arrested and booked on the same charge. The third man involved in the fight was hospitalized after being knocked unconscious, Brown said.
Carrillo, who represents District 5 on the Board of Supervisors, provided a written statement through his office, saying he was in Southern California over the Labor Day weekend for "personal business."
"I was socializing with a group of friends when rowdies approached our group and harassed women in our group," he said. "I stepped in to protect them. I'm anxious to tell my side of the story during legal proceedings."
Police are still investigating the incident, Brown said.
Carrillo is scheduled to appear in court in San Diego on Oct. 15.