Supporters of a man shot in the eye with a pellet gun shouted abuse when the man who shot him was sentenced to four months' home detention.

"You will be seen," a woman called out, waving a finger at Daniel Michael Speer, 21, as he stepped out of the dock in the Christchurch District Court today.

"Are you going to say sorry?" said one supporter.

"It's a bloody farce ... a joke," said another after Judge Raoul Neave's decision to order home detention, 250 hours of community work and an immediate emotional-harm reparation payment of $10,000.

The victim has lost the sight in one eye and the ball bearing remains in his head. He has not been able to work since the August 2010 shooting in central Christchurch.

He was stopped by Crown prosecutor Claire Boshier as he began to read his victim-impact statement to the court when he started to say that "This dude has pretty much ruined my life".

She asked him to stick to the prepared statement. He read a little more but was then overcome by emotion and stopped.

Mental health issues were seen as the cause of the shooting in Hereford St on August 29, 2010.

Speer, aged 19 at the time, had a social phobia and felt threatened when the victim walked past and made a comment about his girlfriend.

He took the gun out of his belt and shot the man at point-blank range, once in the forehead and once in the eye.

The victim was taken to hospital and Speer and his girlfriend walked away. The incident was recorded on a crime surveillance camera and Speer soon gave himself up.

The sentencing took place nearly two years after the shooting because of protracted discussions about reducing the charge and preparing a psychiatric report.

Judge Neave said it was a pity that a restorative justice conference had not been held, although Speer had been willing.

Speer had eventually pleaded guilty to a charge of causing grievous bodily harm with intent to injure.

There had already been a sentencing indication hearing and Boshier said the Crown accepted a home-detention sentence was available.

She said the victim would bear the impact of Speer's offending for the rest of his life.

Defence counsel Jonathan Eaton said the $10,000 emotional-harm payment had been offered and paid into his trust account already.

He said Speer was suffering from serious mental issues at the time. He had undergone treatment since the incident.

"Perhaps that has only scratched the surface in understanding just how unwell he was," he said.

Speer was seen as a low risk of reoffending, was remorseful and had written a letter of apology. He had not targeted the victim that night.

"Anybody could have been in the same position, given his state of mind and sensitivities with the social phobias he was diagnosed with at the time," Eaton said.

Judge Neave gave Speer a first-strike warning under the system that imposes heavier penalties on repeat violent offenders, but he said he did not expect Speer would reoffend.

"This is a case that throws into sharp relief the irreconcilable divisions that often exist in sentencing," he said.

"The defendant, sympathetic and with a significant degree of mitigation, perhaps at worse made an unfortunate decision in a momentary lapse which is out of character.  As a result of that decision, someone else bears the burden of it and carries with him a lasting legacy."

Speer's reaction was out of all proportion when the victim passed them and made "a rather boorish comment" about his girlfriend.

Because of his paranoia he had seen the victim as a threat. It was unreasonable for him to be carrying the pellet gun, but he had done so because of his phobias.

"These events occurred because of a comment which I am sure the complainant will also regret," said the judge.

The home-detention sentence will be served at an address near Sumner.

"There is a perception in the community that home detention is an easy sentence. It's not," the judge said.

- © Fairfax NZ News