"The group now consisting of four attackers began raining punches down on the victim as he cowered while surrounded by the attackers," a police summary said.
Powell-Collins contributed by kicking Grace in the head.
"The victim continued to be punched until finally being brought to the ground where the assault continued on him until his upper clothing was torn from him," court documents said.
Grace sustained two black eyes as a result of the incident and required medical attention.
However, there were no hard feelings towards the original aggressor, it appeared.
"After the assault finished, the victim rose from the ground and was seen to be then embraced by [the 25-year-old]."
Powell-Collins had an innocent explanation for the violence. But one that did not sit well with Judge Kevin Phillips.
"You describe the offending as a play fight," he said.
"I consider you don't understand the actual violence exerted on that day. To describe it as a play fight or part of fitness training you were doing is an absolute and utter nonsense.''
The court heard Powell-Collins was behind bars at the time for a burglary in November 2016, in which he stole two firearms.
He was caught when one of the residents returned to find him loading up his vehicle with their belongings.
Judge Phillips noted criminal history for violence as well as weapons charges.
Counsel Noel Rayner argued his client should be sentenced to home detention so he could support his partner and children while he undertook rehabilitative steps.
However, the judge noted the proposed address had been the site of a domestic incident in which police were involved last year.
Powell-Collins was the alleged aggressor and his partner was intoxicated and unco-operative, he said.
Judge Phillips sentenced the defendant to 15 months' imprisonment.
