The police chief in Mesa, Arizona, says he was "disappointed" by a video that shows officers punching and kneeing an unarmed man.
A police sergeant and three officers have been placed on administrative leave after the May 23 incident at an apartment complex.
While an attorney for Robert Johnson, 33, said he provided no reason for officers to strike him, the Mesa Police Association said Johnson "was not compliant and physically resisted what we feel was a lawful detention."
Police Chief Ramon Batista acted after a community member showed him a surveillance video of the beating a week after the incident, said Detective Nik Rasheta.
The officers are the subject of an internal investigation.
'He was unarmed and then they just attacked'
Johnson was with a friend who police say was trying to enter an ex-girlfriend's apartment, prompting a 911 call, Batista told CNN affiliate KNXV. The responding officer was told of a possible weapon at the apartment.
Johnson lives in the building and was not trespassing, according to his attorney, Benjamin Taylor.
Officers approached Johnson and his friend, searched Johnson, found he had no weapons and asked him to sit by the wall, police said.
In the video, Johnson is seen leaning against the wall and looking at his cell phone before being surrounded by officers and punched multiple times in the head and struck with a knee. He slumps to the ground. Three officers landed blows, police said.
"He wasn't resisting," Taylor told CNN. "He was unarmed and then they just attacked."
Batista said the department will put out a special directive that says officers will not strike anyone in the head who isn't trying to harm them.
CNN was unable Wednesday to speak with the police chief. Authorities were expected to release an incident report and bodycam footage.
Union: Released video doesn't tell the whole story
The chief told CNN affiliates KPHO and KTVK that Johnson's leaning against the wall and what he said to them made the officers feel as though they needed to have him sit down. He did not elaborate on what might have been said. Taylor said Johnson was being cooperative.
"I am disappointed in what I saw," he said of the video, which police released to media on Tuesday. It did not appear to have audio.
The Mesa Police Association, which represents several of the officers involved in the incident, said in a statement that officers were sent to a dangerous domestic situation, and that officers acted to end the confrontation quickly and prevent anyone from falling over a short guardrail.
"We feel it was grossly inappropriate to release a portion of video with no audio that does not include the full context of the encounter. Furthermore, we do not understand why video is being released when an internal investigation has not been completed."
Taylor said Wednesday that his client, who was charged with disorderly conduct, was knocked out and is still in pain two weeks later. "This is going to affect him for the rest of his life."
Taylor said he will ask for charges to be dismissed, given the video. "For them to exert that force on him is unconscionable," said Taylor.
"No matter what age, race and gender you are, police should not be attacking and hurting people when they're there to serve and protect."