Police officer faces court on allegations he assaulted a teen in custody

Samantha Brett 7 News

A police officer has faced the stand in court, defending himself against allegations that he assaulted a teen in custody.

The senior constable maintains he did nothing wrong.

The court was played security video of the 2014 incident at Kogarah police station.

A 16-year-old boy inside a police van had just been arrested over an alleged robbery at Riverwood.

He was bought to the station by senior constable Nathan McNamara who claimed the teen was "screaming and banging on the cage structure."

Security vision shows the teenager being led from the van and into the station.

The prosecutor alleged Constable McNamara forced the boy forward, his head slamming into the doorframe - causing a cut above his left eye.

On Wednesday, Constable McNamara denied any wrongdoing.

"I was trying to get him through the door while he was pushing against me," McNamara told the magistrate.

"His head hit the frame of the doorway ... I didn't push him."

Once he was locked in a cell, the teen was seen lashing out - kicking and spitting.

McNamara testified that even before the alleged incident, the teen was showing "some of the more extreme behaviour I've ever seen in the back of a truck".

But claimed he never intended for him to hit his head.

It's been alleged that once the teen was behind bars, McNamara laughed and said "how hard do you feel now?"

Something he denied during cross examination.

The case returns to court next year.