The attack took place over a distance of 1km between Blackbutt and Shellharbour.

"Mr Chalmers nearly lost consciousness and felt his nose and cheeks go numb from the blows," police said in the fact sheet.

The force of the kicks was so strong they peeled back the skin on Mr Chalmers' right arm and left a shoe print on his back.

Bleeding and dazed, he pulled over outside the 7-Eleven store on the corner of Shellharbour and Wattle roads at Shellharbour.

A motorist who witnessed the ordeal from behind jumped onto the bus and managed to get Elphick off.

Elphick was arrested and Mr Chalmers was taken to hospital and treated for concussion, severe bruising and cuts and tears to the skin.

Judge Conlon yesterday referred to a psychologist's report that cited Elphick's struggle to deal with a deprived childhood. The court also heard that Elphick's son had died from SIDS but he had more recently fathered a daughter, three.

Elphick's employer, Mark Wheeler, told the court Elphick was a diligent worker but needed help and guidance for alcohol abuse.

Judge Conlon described Elphick's background as sad but said it could not be used to excuse his behaviour.

"It is difficult to comprehend how the society in which we live has developed in such a way that innocent victims are subjected to extreme violence every day by offenders who have one thing in common - absolute cowardice," he said.

Judge Conlon said the attack was unprovoked and put other road users at great risk.

He said he had a sentencing dilemma.

Affray carried a maximum sentence of 10 years, but because the related charge of assault occasioning actual harm had been laid and accepted in a lower court he was restricted to a much lesser sentence.

"My early statements on objective seriousness of this matter would require a sentence in excess of this limit but, given the manner in which it has come to this court, a longer sentence is not available to me," Judge Conlon said.

The sentence was backdated to Elphick's arrest in February.