Disgraced former NRL star Craig Field will spend at least the next seven-and-a-half years in jail for a "bone shattering" one-punch attack that killed a 50-year-old cattle farmer during a pub fight, after the state's highest court upheld his conviction and sentence for manslaughter.

In July 2012, the ex-Rabbitoh's playmaker, who also took the field for Wests Tigers and Manly, struck Kelvin Kane in the head during a fight at the Kingscliff Hotel on the NSW North Coast.

Field admitted punching Mr Kane but said he had done so 'out of fear' and denied that his punch was responsible for the brain haemorrhage that caused the 50-year-old's death.

The 42-year-old was charged with murder, but claimed that he had entered the altercation as a "peace maker" after his friend Shaun Fathers and Mr Kane had begun fighting.

He admitted punching Mr Kane but said he had done so "out of fear" and denied that his punch was responsible for the brain haemorrhage that caused the 50-year-old's death.

But a number of witnesses gave evidence that Field was responsible for the fatal blow, with one describing it as "bone shattering".

The jury only partially accepted Field's explanation, finding him not guilty of murder but guilty of manslaughter. 

NSW Supreme Court justice Elizabeth Fullerton sentenced him to a maximum 10 years' jail with a minimum non-parole period of seven years and six months.

Field almost immediately appealed the decision, pointing, among other things, to inconsistencies in the evidence given by a number of witnesses to the fight.

But on Wednesday the NSW Court of Criminal Appeal rejected this argument, upholding the conviction.

"There was undoubtedly some inconsistencies in and between the witnesses' evidence such as what colour clothing Mr Kane's hitter was observed to be wearing, whether Mr Kane was hit on the left or right side of his head and how Mr Kane fell," the three-judge appeal panel said in their reasons for decision.

"However ... such inconsistencies are to be expected, particularly in a case such as the present where those observing the altercation from beyond the car park encountered issues of distance and lighting, and for all witnesses a rapid unfolding of traumatic events.

"The inconsistencies do not, in my view, give rise to any doubt about whether it was the applicant's punch that the witnesses were describing as they all referred to Mr Kane's immediate collapse."

The appeal judges also rejected Field's argument that the seven-and-a-half year minimum sentence for manslaughter was "manifestly excessive".