The forward was referred directly to the judiciary after being sent off during Saturday's clash with the Penrith Panthers in Bathurst.
The incident saw Barnett raise his forearm at Chris Smith off the ball towards the end of the first half of the game.
The Panthers would ultimately win the match against a 12-man Knights outfit, but the fallout and attention since the incident has understandably been on Barnett and just how long his suspension would be.
Barnett pleaded guilty to dangerous contact prior to the hearing commencing, with the judiciary panel consisting of former players Bob Lindner, Tony Puletua and judiciary chairman Geoff Bellew.
The judiciary panel eventually found Barnett guilty of reckless, dangerous contact.
Heading into the trial, Barnett's legal representative Nick Ghabar confirmed they would argue that the incident was only careless, rather than intentional or highly reckless.
In explaining the contact, Barnett said he was attempting to stop it from becoming a three on one situation.
"My focus is to the outside because I know there is a definite threat there. My ultimate goal is to effectively make it three-on-three to stop the try," Barnett said.
"I hadn't seen the player until the last second when he came into my peripheral vision. My goal is to fill the space [between Clune and Bradman Best] without getting knocked over. I just saw a black jersey. I made a split-second decision".
Barnett also insisted that he had made contact with the upper part of the chest, rather than the head of Smith, who was taken out of the game with a concussion.
"I feel like it is the upper part of his chest. That is why it was careless. I wish I didn't raise my arm that high," Barnett said.
"My forearm may have made contact with his head but if it did it wasn't very forceful," Barnett added later in proceedings when under questioning.
The NRL, represented by legal counsel Lachlan Gyles, rejected the claim and suggested the incident was highly reckless, calling for a minimum suspension of eight weeks, and more if the panel believed it was intentional.
Barnett's counsel submitted a claim that the suspension should only be four weeks, while the NRL's counsel mentioned Barnett's previous poor record with six charges recorded against him.