It's all fun and games until someone loses a testicle.

That's the crux of a criminal trial playing out in Sydney's Downing Centre Local Court, where a case of "sack whacking" has pitted two police officers against each other - one as the alleged assailant, the other the victim.

On trial is Constable Paul Michael Vella, 27, who is ­accused of committing grievous bodily harm, ­actual bodily harm and common ­assault on his former workmate, reports

His alleged victim is Gary Stoddart, a 41-year-old leading senior constable who worked with Vella at the Leichhardt Local Area Command.


Both were on duty during May 13, 2015, when the incident that landed both men in court is alleged to have ­unfolded.

Vella's account is that he was sitting at a computer in the muster room of Glebe Police Station when Stoddart, taking a phone call, unsuccessfully tried to "sack whack" him as a joke, which the pair would often do to each other.

A sack whack is ­defined as a backhanded flick or slap of the testicles, ­designed to cause immediate pain.

Vella told the court he leaned forward and retaliated against Stoddart, who didn't show any ­immediate signs of injury.

"It was very light," Vella said.

"It was a flick."

But Mr Stoddart told the court Vella grabbed his testicles and clenched his fist, prompting him to shout in pain. There were no direct witnesses to what happened.

What's not in dispute is what happened afterwards. ­Experiencing constant pain, Stoddart visited several doctors and, eventually, had a testicle removed due to a condition known as epididymitis, the inflammation of tubes inside the ­reproductive organ.

Vella was charged in January last year and suspended from duty. ­Legally, the case turns on ­whether the May incident led to Mr Stoddart losing his testicle.

Vella's barrister, Brett Longville, told the court there was no conclusive evidence of this, and also that Mr Stoddart suffered from pre-existing medical ­conditions.

The court also heard of the pair's larrikin behaviour and practical jokes at the station. Both officers were known to "sack whack" each other frequently.

Other incidents were also recounted: lockers were wired shut with coathangers and boots filled with garbage.

"We're both larrikin blokes," Vella said.

"Policing is a serious job and it's good to lighten the mood around the office."

The case resumes in March.