Protesters are targeting a Lions' match this Friday over Wellington Rugby's decision to keep a contracted player acquitted of a violent attack.

Teenage player Losi Filipo was charged with assaulting Greg Morgan, 21, and his friends, Hayden Williams, 22, Kelsey Odell, 22, and Olivia Samuels, 22, in central Wellington last October.

The 18-year-old was discharged without conviction for the assault last month.

This has horrified his victims and their families who say the teenage rugby star wasn't held accountable for his actions, and his sports career was given priority over the safety of the public.

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Those behind the protest, to be held outside the Westpac Stadium, are encouraging people to show Wellington Rugby what they think of the decision this Friday night before the Wellington Lions' championship game against Southland.

"The court has already made its judgment and discharged him without conviction, but Wellington Rugby needs to know that we don't want violent thugs representing our region on the sportsfield," said a Facebook post advertising the protest.

It warns protesters to remain peaceful and avoid stooping to the violence they're protesting against.

The court case has also sparked a petition on social media demanding justice for Filipo's victims.

It says the decision to not convict the sportsman was "completely outrageous" and there was a need to stand up and show future rugby stars that this was not acceptable.

Mother of victim Kelsey Odell, Karen, said it was time rugby stopped hiding "thugs" and demanded the code change its attitude.

"We want a change. We want rugby to stand up. You can't hide these guys any more."

She said she was overwhelmed by the groundswell of public support since going public about the court result. She said her daughter and her friends still suffered from the attack and there was an overwhelming sense that justice had not been served.

Wellington Rugby chief executive officer Steve Rogers said the situation was difficult for all involved.

"Wellington Rugby is extremely disappointed in Losi's actions and does not condone such behaviour from any member of the organisation regardless of their position or status.

"We have been aware since late last year that Losi was involved in an off-field incident, but delayed any internal investigation to allow the judicial process to be completed.

"Based on the facts made available to us, and the court judgment that deemed a conviction out of proportion to the gravity of the offence, we continued down the path of providing Losi with a support network to assist in his rehabilitation.