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Japan international Mafi was charged with a criminal offence, after an alleged assault of 12-time capped Wallaby Timani following the Rebels' season-ending defeat by the Highlanders the day before.
Mafi was arrested on Sunday following the incident and detained in custody until appearing in Dunedin District Court on Monday.
He was charged with injuring with intent to injure.
Mafi entered no plea and was released on bail.
His case has been adjourned till August 3, but he won't be required to attend in person.
A police spokeswoman told the Otago Daily Times at the weekend the charges stemmed from an episode in South Dunedin on Saturday night. The victim's moderate injuries did not need hospital treatment.
The Rebels have sanctioned them for breaching team protocols and team management instructions.
Under the Rebels' disciplinary protocol, each player has been fined the maximum amount.
"Notwithstanding that both Amanaki Mafi and Lopeti Timani were finishing at the Rebels this season and heading overseas to continue their playing careers, it is only appropriate, given the seriousness of the incident, to sanction both players with a significant fine," Melbourne Rebels Chief Executive Officer, Baden Stephenson said.
"Along with the Rebels board, head coach David Wessels and club management, we have strived this year to rebuild a culture which values respect and excellence in everything we do.
"The actions of these two players is totally contrary to our club's values and has tarnished the excellent work of so many in the club, both on and off the field this season.
"I only hope that both Amanaki and Lopeti genuinely reflect on and learn from this very troubling incident.
"The club has supported both players over recent days and will continue to ensure their wellbeing now and into the future."
Rugby Australia is conducting its own investigation into the incident.
It will await the outcome of the current criminal process under way in New Zealand with Mafi, before deciding on further possible action under the professional player code of conduct.
The $30,000 in fines will be donated to the Rugby Victoria Quilt programme - an education and participation program designed to use rugby as the vehicle to prevent domestic violence.