Mr Dawson, a Sky TV employee, had been celebrating the end of the Rugby World Cup pool play with workmates when he was involved in an altercation at the Viaduct in October last year.
In her opening at trial, Crown prosecutor Natalie Walker said Mr Dawson had bumped in to a man as he left Spy Bar.
She said Mr Dawson had made an unfortunate racist remark before his legs were swept from under him and he was held down and slapped in the face.
Another man put his boot in Mr Dawson's face, before bar security stepped in and broke it up.
Mr Dawson was walking away when Murray approached him and without provocation punched him in the face.
Mr Dawson fell straight back without being able to break his fall and suffered bleeding to his face and a fractured skull. He died the following day in Auckland Hospital.
Doorman Fletcher Porter told the trial that Mr Dawson's head made a "sickening thud'' when it hit the pavement.
Witnesses went to help Mr Dawson while Murray and his friends got into a taxi to continue drinking at other bars.
Police caught up with Murray and his friends in the early hours of the following day.
Ms Walker told the court today that Murray still denied throwing a punch.
Murray's lawyer Andrew Speed had asked the jury to consider that his client only pushed Mr Dawson. He also asked them to consider self-defence.
Today he said his client had intervened to "defuse the situation''.
Mr Speed said the blow was not "extreme violence'' but he conceded it was a heavy blow.
The court also heard from Mr Dawson's brother-in-law, Coen Lammers, who had his victim impact statement read to the court by prosecutor Ben Smith.
He said the death had devastated the Christchurch family.
"Not only has he beaten Billy to death, he has also beaten the stuffing out of all of us.''
Mr Lammers said he had been planning to meet his brother-in-law that night but instead ended up having to notify the rest of the family of Mr Dawson's death.
"For the earthquake ravaged family, the pain was all consuming.''
