Though sceptical, Judge Kevin Phillips imposed six months' community detention, requiring Keach to remain at his home through the weekends.
On June 20, those involved were drinking at a South Otago bar.
When a particular song was played that night, as tradition dictated, the players who were there drinking, pulled down their trousers and danced.
"I don't know why but apparently that's what some rugby players do on a Friday night in Balclutha," Westgate said.
They remained bottomless in the immediate aftermath, standing at a table drinking.
Keach, the court heard, took a pool cue from a nearby rack and approached the victim, who had his back to him.
"He held the pool cue with both hands and with a forceful upwards motion stabbed [it] into the victim's buttocks area," court documents said.
"It then penetrated the victim's anus and continued up the anal canal. A laceration of approximately 8cm resulted."
The man felt a sharp pain and turned around to find Keach grinning at him.
He went to the toilet to assess the damage while the defendant returned the weapon to its rack and continued drinking with his friends.
The victim was bleeding heavily and visited the toilet a few times before taking his revenge on Keach.
A scuffle between the pair erupted and police, who happened to be at the pub, intervened.
The court heard the victim underwent surgery at Dunedin Hospital the next day and was off work for nine weeks.
The treating surgeon said it would have required "significant force" to cause the injury.
Crown prosecutor Craig Power revealed today the wound had not fully healed and the victim was scheduled to have further surgery.
Keach admitted to police he had given the victim a "firm poke with the pointy end of the pool cue" and said he had downed up to seven beers at the rugby club before continuing in the bar that night.
It was "a bit of a laugh", he said.
Keach had no previous convictions and Westgate put the incident down to "30 seconds of madness" during an evening of high spirits.
"He had too much to drink and was acting like an idiot," he said.
"He realises what he did was not a bit of tomfoolery ... [but] there isn't any evidence this was motivated by malice."
Westgate said Keach had no idea he had caused any injury at the time.
"It was one thrust," he said.
Keach had been ostracised by half the local community and would never be back before the court, Westgate said.
The victim, who was not in court for today's sentencing, said he did not want the incident to define him for the rest of his life and remained angry with Keach.
He found the experience degrading and embarrassing, he said.
The victim's mother said she had seen vast changes in her son and was "horrified" by comments that downplayed the seriousness of the incident.
Keach was also sentenced to 250 hours' community work.
