A Christchurch man who admitted throwing a fatal punch has been sentenced to three years and three months in prison.

Anthony Trevor Grafton appeared in Ashburton District Court today for sentencing on a charge of manslaughter after Te-Aritaua Gerrard Brennan, 52, died in hospital 11 days after the unexpected blow caused him to fall backwards and hit his head on a pavement.

Grafton, 41, who had spent 25 years on the streets, pleaded guilty last month to the November 2010 attack, just before the start of a trial in Dunedin High Court.

He was sentenced today by Justice Lester Chisholm, who said the court was once again faced with the tragic consequences of random violence.

Mr Brennan's family reacted strongly outside court, saying the sentence was not right.

His brother Ben said the family would be grieving for the rest of their lives, while Grafton would serve a few years and be out.

We're not happy at all. We had to sit at the hospital for 11 days and watch Te-Aritaua die but that wasn't mentioned, they just talked about how hard of a life he (Grafton) had but our brother isn't here to tell his story.

It's just not right, he said.

The family not only had to deal with the loss of Te-Aritaua but also the loss of his mother only four months later.

His brother David said in an victim impact statement that she passed away due to sadness.

He encouraged Grafton, who has 180 previous convictions to his name, to change his ways and asked him not to do this to another family.

Grafton's counsel Serina Bailey said Grafton had been agitated and anxious when Brennan approached him on November 11, as he was trying to help an unwell friend.

Crown prosecutor Phil Shamy said Mr Brennan was simply in the wrong place at the wrong time.

There is no evidence that Mr Brennan brought this on himself, it was a random act of violence on the street that led to his death, he said.

- Ashburton Guardian