A man who was allegedly assaulted by a police officer in the cells of a Northern Beaches police station has told a Sydney court he feared for his life.

Mark Adamski, 32, was arrested on the evening of Anzac Day last year at his home in Narrabeen.

He told a hearing at Downing Centre Local Court today that he had consumed about six beers that afternoon.

Prosecutors played CCTV video footage taken at Dee Why police station hours later to the court, which they said showed Mr Adamski twice being pushed backwards by Leading Senior Constable Shaun Moylan.

Mr Adamski said on both occasions the back of his head hit the dock wall.

He told the court he instantly felt pain and repeatedly asked officers for medical assistance, but none was provided.

Mr Adamski said he told police: "My head is hurting, I've got pains going down the back of my neck... can you please, please, please get an ambulance."

He said he caught a bus to Manly Hospital after he was released from custody about an hour later.

Moylan has been charged with assault occasioning actual bodily harm.

'Is this the woman basher?' officer allegedly asked

The court was told that before the incident, Moylan asked his colleagues about Mr Adamski.

"He said something along the lines of, 'Is this the woman basher?'" Mr Adamski told the court.

He told the court that he replied: "How dare you accuse me of that. I haven't done anything wrong... Isn't the phrase, innocent until proven guilty?"

Mr Adamski said after the first push the officer muttered words to the effect of, "That'll serve you right you little prick, that's what you get."

He said during the second push, a short time later, Moylan grabbed him around the throat.

"This time was a lot more violent," Mr Adamski said.

In cross examination, Mr Adamski conceded that his recollection of events that night was "hazy" but nonetheless accurate.

"You downplayed your role significantly," said Barrister Ray Hood, representing Moylan. Mr Adamski: "That's incorrect." Mr Hood: "You exaggerated [Moylan's] role." Mr Adamski: "That's incorrect."

The court heard Mr Adamski had been arrested that evening over allegations he had been violent towards his partner.

He said he did not resist arrest but was handcuffed.

The hearing continues.