The man, who did not want to be named, was stopped by police in Burns St, Caversham, at 1pm on Tuesday last week.
In a video sent to the Otago Daily Times, the man is shown being restrained against his vehicle by a police officer in the process of applying handcuffs, when the officer stops what he is doing to punch the man in the back of the head.
The man was stopped because his car had no warrant of fitness or registration.
Police also said the man had no driver’s licence.
The man acknowledged spitting at police and being a "smart-arse", but still felt the punch crossed a line.
"I’m pretty sure you have to use reasonable force — that seemed like excessive force.
"I feel like he did it out of personal feelings.
"He wasn’t having trouble restraining me," the man said.
At the time of the punch, he had been restrained and was no longer resisting, the man said.
"He was in the process of cuffing me, and he stopped cuffing me to punch me and pepper spray me.
"Then he shoved me in the car."
The man said he had made a complaint to the Independent Police Conduct Authority.
In response to questions, a police spokesman said this was an instance in which the video showed only part of what happened involving the offender.
"[He] was aggressive and was warned numerous times for obstruction but refused to comply.
"After the offender assaulted a police officer he was arrested."
Auckland University Faculty of Law professor Mark Henaghan said in regards to the punch and subsequent pepper spray that "police have to use a reasonable amount of force [but] ... being frustrated over someone’s behaviour is not a justification to punch someone".
Prof Henaghan said police must use a reasonable amount of force while restraining someone and punching was not restraining.
"To me, it looks hard to justify."
A spokeswoman said the IPCA had received a complaint regarding the incident and are currently assessing the complaint.
