The trial of a man accused of punching a Sky TV worker so hard his head made a "sickening thud" when it hit the footpath is underway in the High Court at Auckland.

Kit John Murray has pleaded not guilty to a charge of manslaughter following the death of Billy Dawson, 34, in October last year.

Crown prosecutor Natalie Walker told the court on Monday that Mr Dawson had been out celebrating with other colleagues after a busy schedule of covering Rugby World Cup matches.

Mr Dawson had just left Spy Bar in the Viaduct Basin when he was approached by Murray.

Murray put his hand on Mr Dawson's chest and walked him backwards. Without provocation, Murray then punched Mr Dawson in the face.

Ms Walker said witnesses described the sound as his head hit the footpath as a "sickening thud", APNZ reports.

While people went to the aid of Mr Dawson, Murray and his friends got into a taxi and continued drinking at other bars, Ms Walker said.

Mr Dawson died in Auckland Hospital the day after the alleged attack.

Murray's defence lawyer Andrew Speed has asked the jury to keep an open mind and consider the possibility of self-defence.

The trial is set to take two weeks.