The elderly mother of a champion surfer who died after a one-punch attack on the NSW mid-north coast says he was the victim of a "human shark”.

In an emotional victim impact statement read to the Newcastle District Court on Wednesday, the surfer Chris ‘Davo’ Davidson’s sister, Carlie Maudson, said his family had been left devastated by the fatal attack, including her 77-year-old mother.

“She hates you for what you’ve done,” Ms Maudson told the killer, Grant Coleman, younger brother of NSW Waratahs coach Darren Coleman.

“She said he spent all of his life surfing and he was never attacked by a shark but he was taken by a human shark."

Coleman, 43, has pleaded guilty to one count of assault causing death and one count of assault.

The roofer, who has an acquired brain injury from playing rugby, attacked Davidson outside the South West Rocks Country Club about 11pm on September 24 last year.

He had earlier seen Davidson speaking with a 19-year-old woman and called him a "pedophile".

The two men grabbed at each other’s shirts before Coleman was escorted out of the club about 10.36pm.

Coleman was waiting for the courtesy bus to go home when he saw Davidson again and approached him at the top of the stairs. The pair exchanged words before Coleman hit the surfer in the jaw.

Davidson, who had lost the use of his left arm and shoulder from a previous car accident, fell to the ground and hit his head, knocking him unconscious.

He was treated at the scene by paramedics but died a short time later at Kempsey Hospital.

Ms Maudson told the court their mother had started drinking vodka to try to help her sleep and deal with the pain of losing her son who had been her carer.

“Mum will never forgive you,” she told Coleman.

“She says she wants to kill you with her bare hands and she’s all of 35 kilograms.”

In his defence, Coleman told the court he had heard rumours about Davidson’s past behaviour with young girls and was trying to protect the community when he confronted him.

Asked why he stood over the surfer after hitting him, Coleman said: “I realised what I’d done. I wanted him to wake up, to regain consciousness.”

Coleman said he was sorry for what he had done, was a broken man and understood he had no right to do what he did but never intended to kill Davidson.

He said the shame and hurt he had caused his own family for the "heinous crime" would haunt him for the rest of his life.

Defence barrister Simon Buchen SC said the trigger for Coleman’s loss of control was seeing the way Davidson had been acting with the 19-year-old woman.

She claimed Davidson had grabbed her arm, spun her around and was "right up in my face”.

Mr Buchen said what happened to the woman might be described as an indecent assault, with the judge adding it could be "sexual touching".

The barrister said Coleman was acting out of a protective instinct given the rumours he had heard about the surfer and young girls.

A psychological report indicated Coleman’s neurological condition had caused a significant impairment to his impulse control.

Judge Peter McGrath will sentence Coleman on a date to be fixed next year.

Surfing legend Kelly Slater, who Davidson famously beat in two consecutive heats at Bells Beach as a 19-year-old wildcard entrant in 1996, described Davidson after his death as one of the most naturally gifted surfers he had ever met.

Davidson, who grew up surfing on Sydney’s northern beaches, competed on the World Surf League championship tour in 2010 and 2011.

His best result was a tie for third at the 2010 Portugal event, when he was narrowly defeated by Slater, who won the event. Davidson was ranked number 14 in the world at the time.