David Baldwin had been filming a police scene in Leeds on Saturday morning when he was pushed and restrained by officers.
The moment was captured on CCTV, and West Yorkshire Police has confirmed it is investigating whether unnecessary force was used.
Officers were cordoning off a crash scene where three people were arrested in connection with a shooting which had happened nearby earlier that day.
Mr Baldwin, 31, who is in remission after being diagnosed with a brain tumour four years ago, was told to step back from the scene as he filmed it on his phone.
He was then pushed to the ground, while CCTV taken from David's home appears to show the officer strike out at David and grab his throat.
Two other officers then join to restrain Mr Baldwin, with one sitting on his chest, before they arrested him for obstructing them.
David said: "I heard banging and rushed out to see a car crash and started videoing it.
"An officer kept telling me to move back, but I wasn't doing anything illegal to stand where I was."
David was pushed backwards on the pavement, and claims that when he got back onto his feet, the officer in question threw a punch then pushed him against a fence while grabbing him by the throat.
He added: "I've got a big wound on my lip from being pushed onto the ground.
"I was diagnosed with a brain tumour four or five years ago and I'm on medication and get regular scans.
I hadn't done anything wrong - it was totally unnecessary."
David was arrested and spent several hours in a cell at Elland Road police station following the incident on Saturday, before being released later that afternoon without charge.
He has since lodged a complaint with West Yorkshire Police about his arrest, which the force has confirmed is being investigated.
A West Yorkshire Police spokesman said: "A man was arrested on suspicion of obstructing an officer at a scene where armed officers had stopped a car in Ramshead Approach, Seacroft, and arrested three people in relation to a firearm discharge in Kentmere Avenue, Seacroft, on Saturday (11/1).
"He was later released without charge.
"A complaint has been received by the Professional Standards Directorate who will investigate the matter."