For the latest update on this story, see: Violent arrest video warrants investigation, says civil liberties association

An eyewitness is challenging the Calgary police version of events after some officers' altercation with a man on Friday night went viral after being caught on video.

"If they are saying this guy deserved that? Not a chance, not a chance," the witness said.

CBC News is not identifying the witness because of fears of possible retribution, but CBC News can confirm the witness is in a position to have seen the incident.

A 21-second video was posted to Instagram Friday night which appears to show one officer throwing a man to the ground and punching him several times in the face while two other officers hold the man down.

Police said in a statement Saturday the officers were doing a walk-through of bars in the area when they were tipped off something was going on outside of the 1410 World Bier Haus Restaurant & Lounge on 17th Avenue S.W.

"They were immediately approached by an aggressive man who refused to cooperate with their demands and then attempted to leave the area. This man had exited his vehicle following a road rage incident involving a pedestrian, and refused police requests to provide information about his identity," police said.

"This video only captures a small portion of the interaction between the man and the officers and does not tell the full story."

No further comment

Calgary police explained the reason for the arrest in their release.

"This man was given a ticket for stunting after driving in an unsafe manner along the roadway and was released following his arrest," police said.

"The CPS encourages anyone with a concern to file a complaint with the Professional Standards Section."

Police said in the statement "No further comment will be made," and CBC News contacted police informing them of the witness but they declined to answer questions.

The witness says it was police who indirectly contributed to the incident.

The witness said the gang unit came into the restaurant and asked for identification from a table of 10 men. When one of the men did not produce ID, the witness claims police said the entire group had to leave.

Three of the men crossed 17th Avenue cutting off a man driving a truck, the witness said.

"The driver honked his horn at them angrily and one of the guys in the group flicked a cigarette at the truck. He screeches over to the side of the road and gets out of his truck and starts yelling at the guys across the street," according to the witness.

The witness estimates the driver is about 60 years old and 150 pounds.

The witness said one police officer heard the tires screeching and the yelling and came outside.

'Get the f*** back in your truck'

"He went straight for the old guy and starts yelling at him. 'Get the f*** back in your truck, get in there now,'" the witness said.

"This old guy starts walking, the cop is walking right behind him yelling at him the whole time. He didn't even know what was happening. They get 10 steps in and I guess maybe the old guy stopped or something so the cop grabbed him. Next thing I know the three of them are laying the boots to the 60-year-old guy on the side of the road," the witness said, adding the Instagram video begins at this point.

"I watched the whole thing."

(The witness meant "laying the boots" as a figure of speech: the officers were not seen kicking the man.)

Video viewed thousands of times

The video had been viewed thousands of times by Saturday evening, attracting hundreds of comments.

"There is no excuse or justifications for punches to the head," wrote one viewer.

"He's not even fighting back. He's protecting his face," wrote another.

Some of the comments are supportive of police actions, arguing the short video tells only part of the story.

The witness said the driver could have responded differently, but he didn't deserve what happened next.

"He did absolutely nothing. He shouldn't have gotten out of his car, absolutely, and he should not have been yelling, absolutely but that doesn't mean you get beat up by a cop," the witness said.