At Pomana's sentencing in the Whanganui District Court, Judge David Cameron said Mr Crozier was living with his partner, his partner's daughter and her boyfriend in June last year.
The daughter was outside on June 4 drunkenly swearing at passersby and children playing. She drew a crowd, which included Pomana - a patched Black Power member - and some fellow gang members.
A woman got into a fight with the daughter, and the daughter's partner came out to pull his girlfriend away.
It was then that Pomana and six of his associates began to "taunt" the man, challenging him to a fight, Judge Cameron said.
Mr Crozier saw the other man getting surrounded, and tried to hold Pomana back.
Pomana turned around and elbowed him in the face, then punched him and broke his nose.
Mr Crozier fell to the ground, unconscious, and three people including Pomana continued to attack him, Judge Cameron said.
They kicked and hit Mr Crozier as he lay on the ground.
One witness described the attack as "legs coming from every direction".
"When they had finished kicking Mr Crozier, the defendant and the two associates started to walk away.
"One returned to stomp Mr Crozier in the head with a great deal of force."
He was lying face down on the ground at that point, still unconscious.
Pomana, 25, had an "extensive" criminal history ranging from 2007-2014, with five previous convictions for violent offending.
In a pre-sentence report for the latest offending, Pomana was assessed as being at a high risk of reoffending.
"He claimed that the incident happened because the victim got in the way, which demonstrates a lack of insight into his own behaviour," Judge Cameron said.
Pomana, who pleaded guilty to wounding with intent to injure, was sentenced to 21 months in prison with six months post release conditions.
After the sentencing, Mr Crozier told the Chronicle he went out to the prison for a Restorative Justice conference with Pomana.
He said he "had a talk to Michael, and he was very, very sorry for what he had done".
"I've also written to Michael, you know, just saying there's no hard feelings from my side ... we parted on good terms.
"I feel that he's going to head down the right track now. At the end of the day he's a father of four children and he sort of should be there for them."
Mr Crozier said he had been assured by Black Power members that there would be no retribution against him.