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The Eels say they have conducted a full investigation into the incident that took place over the weekend outside the Tunnel nightclub in Kings Cross, and have cleared senior player Maitua of any wrongdoing.
Anderson, 18, has had his contract terminated for punching Maitua to the ground.
It's the second up-and-coming talent the Eels have sacked in the past week, after they also tore up the contract of Jamil Hopoate for bad behaviour at an NRL rookie camp in Sydney.
Eels chief executive Ken Edwards said the club would continue to take a hard line.
"I make no apology for the club's firm policy on player behaviour,'' Edwards said in an Eels statement.
"When a player signs with Parramatta, they acknowledge the high standards of behaviour expected. Our players need to be committed to the club, their teammates, our members and supporters.
"As a club we will continue to strive for excellence and foster a culture of respect, inclusiveness and teamwork.''
Anderson claimed on Channel Nine that the Eels had showed favouritism by clearing Maitua, who is being touted as a future captain of the club.
"I thought he was about to deck me ... so I stood back and hit him first and that's what happened. And then he was out cold on the ground,'' said Anderson.
"It's an NRL player's word against an under 20s player's word. Straight up they're going to pick the NRL player aren't they?''