A review is underway into the actions of Calgary police officers involved in a violent arrest that was caught on video, Chief Roger Chaffin says.

The 21-second video posted to Instagram on Friday shows an officer throwing a man to the ground outside 1410 World Bierhaus Restaurant and Lounge before punching him at least twice while two other officers help restrain him.

"As a result of the circulation of this video, we have seen considerable concern from the public, the media and both local and provincial government," said Chaffin in a release sent to media on Monday.

"That public commentary demands a response from the service and allows us the opportunity to review what happened and address these concerns. As such, a review of this incident is now underway."

Chaffin said the video does not tell the whole story and that officers are required to make split-second decisions.

"We are only seeing the end of this confrontation — a 20-second video clip — that shows the culmination of many factors leading up to this interaction," he said in the statement.

Chaffin also said the police service has alerted the Alberta director of law enforcement "due to the serious and sensitive nature of the issue."

The chief's statement was quickly followed by a release from Howie Shikaze, the chair of the Calgary Police Commission.

"As part of the commission's role to provide independent oversight of the investigative process, we will closely monitor this investigation, as we do with all investigations, to ensure it is appropriate, fair, and thorough," he wrote.

Civil liberties

Kelly Ernst, the president of the Rocky Mountain Civil Liberties Association, told CBC's Calgary Eyeopener earlier on Monday that an investigation should be launched.

"Investigations really just lead to building confidence in our police force. The chief of police, in our event we had just a couple weeks ago, was very clear that all the training in the world does not guarantee that all the police will be perfect all the time."

Calgary police issued an earlier statement over the weekend saying the officers were doing a foot patrol inside a bar when they were alerted to an incident unfolding outside.

​"They were immediately approached by an aggressive man who refused to co-operate with their demands and then attempted to leave the area," the statement reads in part.

"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 the man was given a ticket for stunting and was released following his arrest.

Witness disputes police version

A witness disputed the police version of events, however, saying the officers escalated things unnecessarily.

CBC News is not identifying the witness because of fears of possible retribution.

"He went straight for the old guy and starts yelling at him, 'Get the f--k 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 meant "laying the boots" as a figure of speech: the officers were not seen kicking the man.)

'I don't see anything inappropriate,' prof says

A professor of justice studies at Mount Royal University said he didn't see anything particularly wrong with the way officers handled the arrest.

"In terms of the technique, I don't see anything inappropriate at all," Doug King told the Calgary Eyeopener.

"Certainly the officer closes his fist and punches the individual on the top of the head a couple of times, but anyone who knows anything about physical violence and punching, that wasn't a punch of much force, that wasn't a punch of much violence, that was to get the guy's attention."

The video doesn't tell the entire story, said King.

"The video can help us understand did the officers use an appropriate technique in terms of use of force, but it cannot tell us did the officers use appropriate judgment to begin to escalate force — and I think that's where things are getting confused," he said.

Use of force policy needs outlining

Police should outline when and how much force is justified during an arrest, said Ernst.

"Certainly police are able to use force, but the Supreme Court decisions have been fairly clear in these matters — it has to be proportional and there has to be very good reasons for using that force, including protecting the public or protecting themselves," he said.

"We have to look at all of the evidence around this particular case but it's something the police service has to respond to. We can only ask the questions, we can't make conclusions without asking those questions first."

Premier Rachel Notley was asked about the video during a stop in Calgary on Monday.

"It's obviously disturbing. But quite honestly, it's a question of looking at the whole context. But given that it is a matter that will undoubtedly be debated on by law enforcement people, I really can't comment at this point," Notley said.

"At this point, there's a process in place and we need to let that process work without the premier commenting on it or engaging in it," she added.