A Santa Rosa man has been arrested on suspicion of assault with a deadly weapon after police say he punched and stomped an unconscious victim during a fight in downtown Petaluma early Saturday morning.

Police said the suspect, Mark Robert Ainger, 22, had a blood-alcohol level of nearly 0.15 percent, almost twice the limit at which it’s legal to drive. Because he is on probation for a 2015 drunken driving conviction, he is prohibited from consuming alcohol, authorities said.

But what landed him in trouble around 2:20 a.m. Saturday was a fight at Petaluma Boulevard North and B Street, where his opponent was rendered unconscious on the street with a bleeding head, Petaluma police said.

Witnesses told officers Ainger had punched the victim several times in the face, causing him to lose consciousness and fall to the ground, where Ainger punched him more and stomped on his head, police said.

The victim was still unconscious and his head bleeding when officers arrived, police said. His name has not been made public.

Witnesses directed the officers toward D Street, where Ainger had gone, and identified him as the victim’s assailant, authorities said.

In addition to assault with a deadly weapon, Ainger was arrested on suspicion of violating probation, and he was booked into the Sonoma County jail, police said. Ainger was released Saturday after posting bail.

The victim was taken to Petaluma Valley Hospital for treatment, police said. No update on his condition was available.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.