Paul Newburn fatally stabbed Glen Smith with a knife taped to the end of a curtain pole, after his victim jabbed at him with a golf club with a missing head.

He pleaded guilty in the Newcastle Supreme Court to Mr Smith's manslaughter, on the basis of excessive self-defence, on January 20, 2019 at Bolton Point, Lake Macquarie.

The 34-year-old was jailed in December 2020 for nine years with a non-parole period of five years and nine months.

The NSW Court of Criminal Appeal on Wednesday reduced his term to seven years and six months, with a non-parole period of four years and six months.

It found the sentencing judge erred in assessing the seriousness of the offence by failing to have regard to Newburn's perception of the threat he faced at the time.

"The events which led to the confrontation between the applicant and the deceased were relevant only insofar as they provided context to the actual offence," the court said.

But those events were "integral to and formed the basis" of her assessment of the seriousness of the offending as "objectively grave".

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On January 20, Newburn's partner Lisa Walker told him she wished to end their relationship and after an argument, left their home without taking any property.

Following a public argument, nearby neighbours called out to Newburn to leave her alone and she was escorted to Mr Smith's home, for her protection.

Newburn turned up at the house an hour later to speak to Ms Walker but instead argued with Mr Smith who was overheard threatening to bash him.

Soon after, Ms Walker and a neighbour turned up at Newburn's house when the couple argued before Mr Smith, who had been drinking, jabbed the golf club shaft through the screen door.

He smashed pot plants out the front, before Newburn armed himself with the homemade spear and confronted Mr Smith outside, jabbing it at him.

When Newburn stabbed Mr Smith in the upper right thigh, he called out: "You have got me in the nuts you f***en dog c***".

Mr Smith then attempted to stab Newburn with the golf club shaft but he avoided the blow before stabbing the victim in the left side of the chest, penetrating through the fifth rib into his heart.

Newburn's lawyers argued that his perception of the situation included the fact that Mr Smith was armed, had just attempted to strike him and his aggression was not curbed after being stabbed in the thigh.

The appeal court noted Newburn's evidence that he had felt afraid.

He said he feared the people outside were going to come into the house by breaking down the door before he fought with Mr Smith outside and eventually inflicted the fatal injury.

"There is no doubt, and the applicant accepted by his plea, that that was not a reasonable response in the position in which he was," the court said.

But having regard to his fear and his perceived threat and the judge's finding that he did not intend to kill Mr Smith, it was not open to her to find his response "very significantly exceeded a reasonable response".

In re-sentencing Newburn, the court noted his remorse and his significant steps to address his long-standing drug addiction.

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