Homeless man 'choked' at WA lock-up

A homeless man was "a little mouthy" towards police before an officer grabbed him by the throat and slammed him to the ground during a strip search at a lock-up, a Perth court has heard.

Sergeant Lachlan Nairn Boath is on trial in Perth Magistrates Court accused of assaulting Clinton Nicholson in June 2012 at the Perth Watch House where he was the officer in charge.

Mr Nicholson testified on Wednesday that he was a homeless drug user at the time and his memory was "hazy", but remembered feeling agitated about being detained and admitted being "a little mouthy" at police.

While he was being strip-searched, Mr Nicholson threw an item of clothing at one of the two officers in the room and then Boath "charged" at him.

"I was slammed to the floor with his hands around my neck," he said.

"I couldn't struggle ... I was trying to remain conscious."

Mr Nicholson said he was gasping for breath and tapped his fingers on the wall to signal his surrender.

The alleged choking lasted up to 20 seconds, leaving the victim in shock.

Mr Nicholson said he refused to give a statement because he did not want to be a "dog" but later changed his mind.

Prosecutor Kirsten Nelson said in her opening address that Boath and Mr Nicholson were involved in a "verbal sparring match" in the reception area and Boath baited Mr Nicholson.

She said Boath then took Mr Nicholson into the strip search room where there were no security cameras "to teach him a lesson".

Ms Nelson said Boath assaulted Mr Nicholson without provocation and it was not self-defence.

"His actions were deliberate and controlled," she said.

Boath's lawyer Linda Black said in her opening address that her client never attempted to strangle anyone and disputed details of the incident.

The trial continues.