Teenagers were warned after jumping on to moving trams in Sheffield last night.
The three-17-year-olds were seen carrying out the ‘dangerous’ act by Special Constables from South Yorkshire Police.
It was one of many incidents the force’s team of special constables carried out and which were reported online to show what the volunteer police do.
The also helped a man who was ‘suffering’ after he had taken what was believed to be so-called ‘legal highs.’
A 44-year-old man was arrested for shoplifting sweets in Rotherham and a special constable attended a pub in Kimberworth Park where there were reports of a disturbance.
They reunited two children, aged four and seven, with their family after they became separated while shopping and also chased a shoplifter in Doncaster town centre until he was held.
In Worksop they assisted police in stopping young people throwing stones and in Barnsley they helped to dismantle a small cannabis growing set up.
Patrols were carried out across the county and buses checked for anti-social behaviour.
South Yokshire Police tweeted: ‘We thank all of our special constables for their hard work as volunteers.”