A woman and a girl are in custody after a huge brawl broke out during a Mandurah basketball game on Tuesday night that left a referee in hospital.
Police said 15 vehicles attended the incident at 6.40pm involving about 60 people, including adults and children, at an under-13 girls basketball match at the Mandurah Recreation Centre.
A 58-year-old male referee who tried to break up the argument was bitten on his forearm and taken to Peel Health Campus, before being discharged later that evening.
At about 9.30pm the same night, another disturbance involving about 15 people linked to previous groups occurred outside a residence on Duncan Street in Coodanup.
On Wednesday afternoon, police had taken a 17-year-old girl and a 35-year-old female into custody, but no one had been charged.
WA Police Acting Superintendent Dean Snashall said simmering tensions between the families came to a head after mediation efforts by police on Friday last week were unsuccessful.
Acting Superintendent Snashall said the tension started with the children of the families after recent incidents at Coodanup College and the Billy Dower Youth Centre.
"It's a complex situation and we understand these issues won't be solved in a day," he said.
"The actions last night are not the way to deal with it."
Acting Superintendent Snashall said the priority for police was to protect innocent people in the community.
"We treat the location and the level of violence very seriously," he said.
"There was community at risk last night, young children. The environment was very public.
"We will not tolerate that behaviour occurring in such a public area.
"Detectives will leave no stone unturned in locating the people (involved) last night.
"I can guarantee you arrests will be made."
City of Mandurah chief executive officer Mark Newman said the behaviour displayed during the incident was "completely unacceptable".
"It is unfortunate this altercation occurred at an organised sports event within our facility," he said.
"We are assisting Police with their inquiries and providing as much support as possible to the Mandurah Basketball Association in light of this matter."
Senior Sergeant Rob Lewis said both the Mandurah Police and Mandurah Detectives were working together to investigate the incident.
Police would like to speak to anyone who saw the incidents and anyone with information is urged to call Crime Stoppers on 1800 333 000 or report online at www.crimestopperswa.com.au.
Members of the public living or travelling in the area that may have CCTV or dash-cam footage are asked to upload it to this website: https://wapf.au.evidence.com/axon/citizen/public/disorderly-incid-mandurah.