Children who play sports are more likely to break the law than less active youngsters, according to remarkable new research by Scots scientists.

Despite the widespread assumption by parents, police and politicians that sport is part of the answer to juvenile delinquency, the Glasgow team suggests that taking part in activities such as football can increase off-pitch aggression.

The psychological study of almost 170 teenagers – boys and girls – suggests that rather than acting as a release valve for anti-social tendencies, sport can reinforce rule-breaking behaviour.

The Glasgow Caledonian University academics are now calling for further research into the true effects of sport on behaviour. Their findings, published in a criminology journal, support growing anecdotal evidence that physical exercise may not always provide an answer to society’s ills.

Jodi Burton and Dr Lisa Marshall, from the university’s Department of Psychology, questioned 169 Glasgow pupils aged between 14 and 15 about their extra-curricular activities, including listing their favourite sports and hobbies.

They then set the youngsters a standard series of more than 100 questions to assess the teenagers’ aggression and rule-breaking behaviour.

Burton and Marshall found that rather than being protected by sporting activities from misbehaving, children who played sport were more prone to aggressive behaviour, such as arguing, fighting and vandalism.

"Our results suggest participation in extra-curricular activities does not act as a protective factor for youth," said Burton.

"Gender and participation in sports were strong predictors of rule-breaking behaviour. A significant correlation was found between participation in sports and involvement in aggressive behaviour.

"This school was in an area of Glasgow that drew students from a diverse range of socio-economic backgrounds. Occupations of some of the parents included skilled trades, managers and associate professors."

The general view is that participation in sports and clubs provides a protective effect for at-risk youths, as it keeps them occupied, providing less time for them to get into trouble.

But sporty youngsters were discovered to be 2% more aggressive than those with non-sporting hobbies.

And, surprisingly, while boys played more sports, the researchers found girls who did so were just as aggressive.

The study also revealed that boys who played sport were nearly 4% more likely to break rules – involving truancy, using drugs and alcohol, and stealing – than their female counterparts who didn’t play sport.

Burton said participation in sport may serve as an additional risk factor, particularly for those youngsters already considered vulnerable to committing crimes.

Sport has long been regarded as a key to solving the anti- social behaviour that troubles communities across Scotland. Hundreds of projects have been introduced encouraging youngsters to play football, join boxing gyms and compete in basketball competitions.

Strathclyde Police has been instrumental in setting up schemes, with one, called Coaching Kids off the Streets, being launched at Holyrood Secondary School in Glasgow’s Crosshill area this month.

In Edinburgh, community police officer Mark Thomson has set up a youth football team in the city’s deprived Bingham estate. He claims vandalism has been cut from 100 cases a year to eight, while fights have dropped by 80%.

But the Glasgow Caledonian research suggests this tactic may not be as effective as its supporters believe. Experts point to the off-pitch violence that follows professional footballers. Former Leeds United and England player Jonathan Woodgate was found guilty of affray following a street attack on a student in Leeds city centre in January 2000.

Dr Marc Jones, a sports psychologist at Staffordshire University, said he had long believed on-pitch competitiveness could spill over into off-pitch aggression.

"This research is very interesting. It is right to be cautious about bluntly believing that taking part in sport will always be a positive thing," he said.

Detective Chief Superintendent John Carnochan, head of the violence reduction unit at Strathclyde Police, said he still believed sport was a valuable way of diverting young people from criminal activities.

He said: "It’s important that alternative opportunities are accessible to divert young people away from potentially engaging in violent behavior."