A former police officer has been described as a "thug and a coward" by the 75-year-old man he beat up.
Iain William Milne, 66, appeared in the Dunedin District Court this week, where he was jailed for 15 months on a charge of injuring with intent to injure.
Because the defendant had been in jail since the October 1 incident, he would be released within weeks, the court heard.
Within months of breaking up with his partner of eight years, Milne saw her in a Balclutha supermarket with a new man.
Later that evening, in a state of distress, Milne drove to the Kaitangata home he and the woman had previously shared.
He verbally abused his ex-partner and when her new boyfriend emerged, told him to clear off.
"You had no right to tell him anything at all," Judge Kevin Phillips said.
"You totally lost the plot."
When the man remained in the doorway, Milne erupted.
"You knocked a 75-year-old man to the ground and stood over him, striking blows to his head and torso as he lay unable to defend, resist or protect himself. He was highly vulnerable," the judge said.
Once the assault was over, Milne returned to his car and headed towards his home in Balclutha. But the drama was far from over.
As the victim was being rushed to hospital in an ambulance, police searched for the defendant.
They found him heading back towards Kaitangata.
When Milne returned to the address, he leapt over a fence and began banging on the windows.
Police called for back-up and arrested Milne, only after threatening to taser him.
The victim required numerous stitches to a severe facial lacerations and he spent months on painkillers.
"He feels vulnerable, he has had counselling and he would describe you as a thug and a coward," the judge said.
Counsel Andrew Dawson said his client planned to move away from South Otago when he was released.
He highlighted a report which noted Milne may have PTSD from his experiences serving as a police officer.
Judge Phillips said it was a difficult task to sentence a man in his 60s to imprisonment for the first time but he had no other option.
He ordered Milne to pay the victim $1000 within two months of his release.