The video shows Vancouver man Andi Shae Akhavan being struck in the face by an officer for "resisting" being handcuffed when he was arrested on allegations of running a red light and not wearing a helmet while riding his bicycle.
"With both my arms behind me and from behind, he basically clocks me in the mouth, at which point you can see in the video, I basically felt my tooth kind of go through my lip," he said.
"I'm a non-violent person, haven't been struck in the face before, have never struck anyone in the face before. (I'm) surprised that my first experience happened with a police officer doing it."
He said two plain-clothed officers were writing him a ticket for running a red light and, after talking amongst themselves, started to handcuff him.
Akhavan's friend then came over and started filming the arrest.
The video shows one officer telling Akhavan's friend to move away, and that he can watch but not to interfere.
Akhavan turns to ask the officer why he is being arrested.
The officer tells the man not to pull away, then reaches around the man and punches him in the face with a closed left fist.
When Akhavan cries out that he's bleeding and asks the officer why he punched him, the officer responds: "I was trying to put handcuffs on you and you pulled your arms away. I told you not to resist."
Akhavan complained to the Vancouver Police Department, saying the punch was excessive force.
The police department said its professional standards section is investigating as well as the police complaints commissioner.
Michael Vonn of the B.C. Civil Liberties Association said the video leads to questions about whether the punch was an unnecessary and violent overreaction.
"We understand that the VPD is investigating this incident," Vonn said in a news release. "Given the poor history of police investigations of alleged police misconduct in this province, we will be watching this investigation and its results very closely."