Fainu was found guilty in August last year of wounding Faamanu Levi with intent to cause grievous bodily harm at Wattle Grove on a night in October 2019.
He received a maximum jail sentence of eight years with a non-parole period of four years and three months.
During the 10-day trial, one witness testified to seeing Fainu plunge a steak knife into Levi’s back during a car park brawl.
In his appeal, Fainu’s lawyers argued the witness testimony was unreliable as it was at odds with the balance of the evidence.
They argued the witnesses could have been influenced either by each other or by an image they looked up online afterwards of Fainu wearing a sling, which was later used to identify him.
“There were multiple other males involved in the altercation who could have been responsible for the stabbing,” they argued.
But Justice Natalie Adams, one of the three judges who upheld the conviction, said there were some inconsistencies in witness evidence but overall there was enough proof to implicate Fainu in the stabbing.
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“I am satisfied … that upon the whole of the evidence it was open to the jury to be satisfied beyond reasonable doubt that the applicant was guilty,” she said.
The stabbing occurred after an earlier fight on the dancefloor of an alcohol-free charity event organised by the Church of the Latter Day Saints.
The jurors were told Fainu and a friend known as “Big Buck” were involved in the fight and ushered outside by Levi, who told them not to fight on church grounds.
Although Levi was unable to identify who stabbed him in the back, CCTV footage showed Fainu and his four friends returning to the car park where the brawl occurred.
Two witnesses identified Fainu as the assailant by the sling, which he was wearing for a shoulder injury.
In 2019, Fainu was on track to earn a massive salary as a promising rugby league player with the Manly Sea Eagles, however was dropped due to the National Rugby League’s no-fault stand-down policy.
He played 34 games for the club and one international for Tonga.