An off-duty police officer who stepped in to help a woman who claimed her phone had been stolen was attacked by a group of teenagers at a busy outdoor shopping center in California on Black Friday.

The assault – which was captured on video – happened around 8 p.m. at the Bay Street Mall in Emeryville, located next to Oakland. The Emeryville Police Department said Monday a woman seen in surveillance video wearing white clothes approached a group of teenagers and accused them of taking her cellphone minutes earlier.

"She confronted them asking for her phone back. During the confrontation, the juveniles got aggressive with the victim and began to assault the victim," Emeryville Police Detective Jaime Pardo told reporters.

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After spotting the commotion, a California Highway Patrol officer – who asked to only be identified as Greg B. – approached the group and tried to secretly take photos until one of the girls in the crowd noticed what he was doing.

"The group then turned toward him and became violent with him," Pardo said.

In the video released by officials on Monday, one of the teenagers runs at the off-duty officer and hits him. Another boy then punches him as he runs off until he is surrounded and attacked again. A security guard can be seen getting knocked down in the video while trying to respond to the unruly group.

An attack involving an off-duty California Highway Patrol officer and a group of teens at a mall on Black Friday was caught on camera. The officer said it all started after a woman accused the group of teens of stealing her cellphone. (Emeryville Police Department)

"It was a melee. It was chaotic. It was a really scary situation," Greg B. told KTVU. "It should have never gotten to this point."

The officer said he tried to run away, but the teens surrounded him.

"But I know that when I let him go, he's going to swing at me. And I let him go. I push him and sure enough, he turns around and swings at me," he told KTVU. "I back up and that's when one of his friends came up behind me and struck me in the back of the head."

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The officer, a former correctional officer at San Quentin Prison, said he never drew his gun during the incident. His girlfriend alerted mall security that he was an off-duty state cop.

"There was a lot of restraint that had to be practiced," he told KTVU. "And I had to do my best to stay in the moment."

Off-duty California Highway Patrol Officer Greg B. said he practiced "a lot of restraint" during the assault. (KTVU)

Greg B. sustained a concussion, a broken finger and bruises after the assault. He said it was the third time he had to help someone at the shopping center.

"I think this just came down to me not being able to look away and let this happen," he told KTVU. "I saw this young lady and she was going to be in a very bad situation."

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The Emeryville Police Department said Monday that two juveniles, ages 14 and 16, were arrested while six others are still being sought, according to KGO-TV.

Authorities are hoping to use surveillance video to assist in their investigation, and are asking the public for help in submitting and videos or photos from the Friday night incident.