It is a “matter of time” before someone is killed because of off-road motorbikes being ridden illegally in Cardiff, South Wales Police have said.
The force is asking residents to be its “eyes and ears” to curb the problem.
In July, 84-year-old John Miller was badly hurt after a hit-and-run incident in the capital when a rider allegedly lost control while “pulling a wheelie”.
A joint project between Cardiff Council and the police has confiscated and destroyed 38 bikes since 2017.
The force has urged the public to share information and pictures of anti-social bike use so they can identify those illegally riding powerful off-road motorcycles and quad bikes.
Sgt Duncan Mitchell, from South Wales Police, said they were not “small, children’s scrambler bikes”.
“Often riders aren’t using correct protective equipment,” he said. “They’re riding on a road at speed, again without helmets, without any safety equipment. It puts them at danger. It puts others at danger.”
St Albans RFC has had problems with off-road bikes on and around their pitch on Tremorfa Park.
Team manager Ian Watkins, who has been involved with the club since 1976, said they had been “plagued” with off-road bikes trespassing on the park.
“[They’re] riding onto the pitches, damaging the pitches and causing a hazard and danger to all park users, particularly our younger section,” he said.
Mr Watkins said: “It can be intimidating, there’s been occasion where some of the riders are actually goading members of the public and goading the police when they attend.
“I think the worst occasion was six bikes on the park.
“It only takes one accident for somebody to be hurt, God forbid fatally injured.”
Since 2017 the police and council have been collaborating on Operation Red Mana, aimed at tackling the illegal use of off-road bikes.
Local authority officers ride on off-road motorcycles, while the police follow in cars to discourage would be offenders.
Tim Morgan, operational chief inspector for the west of Cardiff, told BBC Radio Wales Breakfast police also use drones, helicopters and road units to catch riders.
He said it can be a “very difficult” task, as “riders will often cover their faces and won’t often stop for the police”.
They aim to confiscate as many bikes as possible.
All 38 riders whose bikes have been confiscated in the last two years were handed anti-social behaviour referrals – 29 of them were found to be driving without insurance.
Sgt Mitchell said they were not trying to be killjoys but needed people to be aware of the dangers.
“We need [the community] to be our eyes and ears on the ground, not only telling us about the problem but who is responsible, what bikes are being used and if possible sharing any pictures or images with us,” he said.
“We need to identify who these people are and where the bikes are stored so we can deal with the problem fully,” Sgt Mitchell said.
“I will stress never to put themselves in danger when they’re doing this, but share anything they know.
“It’s not just people popping wheelies and doing skids in a park and tearing up fields, it’s fatalities.
“These parks are being used by young children and it’s a matter of time before we get a fatal accident involving a young person.”