It was revealed yesterday that he had recently returned to New Zealand and was temporarily living with his ex-partner at Taieri Mouth on the morning of February 21.
The pair began arguing about the man's alleged drug use and the victim started to move his belongings outside.
Roker struck her in the head with his elbow and then hit her with an open hand, bruising her face, Mr Smith said.
Two hours later, the victim's father came home, saw her injuries and confronted the defendant, telling him to leave the property.
Roker began "ranting" about who was at fault then attacked his ex-partner's father.
He managed to block an initial blow and the pair tussled on the floor of the lounge. The victim eventually gained the upper hand.
Roker ran from the house to where his belongings had been piled, at the bottom of some steps.
"He removed a large machete from his belongings, raised it above his head and ran at both victims who had followed him down the landing," a summary said.
Roker aimed his blow at the man's head but he raised his left arm to block it.
"The machete sliced through the victim's arm, severing it just above the left wrist," the court heard.
The female victim shielded her father from further injury and took him inside to the bathroom.
She tried to hold a door closed to prevent Roker gaining access but he smashed a glass panel with the machete.
However, when he reached the bathroom and saw the damage he had caused, the defendant "calmed down" and provided first aid, which included applying a tourniquet to stem the blood flow.
The court heard how the 60-year-old man required "extensive surgery" and the long-term prognosis was unknown.
In interviews with the police, Roker claimed he had grabbed the machete because he was afraid of the man.
He expressed "extreme remorse" the incident had occurred, the summary said.
Justice Nation granted a protection order in favour of both victims and gave Roker a first-strike warning.
He will be sentenced in July.
