These are two of the main findings from a study of 1,000 young people in New Zealand, a country noted for its obsession with keeping fit. The findings challenge the belief that sport builds character - or, to put it less positively, that sport channels energy that would otherwise be misused.
The study, carried out by Dr Dorothy Begg and others at the University of Otago in New Zealand, found boys who did a lot of non-team sports at 15 were almost twice as likely to be delinquent at 18 as those who did little or no sport in their early teens.
The link was even more marked among girls. Those who did a lot of non-team sport at 15 were almost three times as likely to be delinquent at 18 as their unsporty peers.
Even those girls who participated in a moderate amount of sport were more than twice as likely to be shoplifting, stealing cars or fighting as those who did no sport.
The researchers point out, however, that the best predictor of delinquency at 18 is delinquent behaviour at 15, regardless of involvement in sport activities.
The study's failure to find a link between team sports and delinquency appears to disprove the "athletic delinquent" theory, which suggests delinquent behaviour results from exposure to certain organisational systems, such as the presence of older delinquents in a team. The sports where high correlations with delinquency were found were those such as aerobics, athletics, cycling, dancing, skating and martial arts.
Writing in the British Journal of Sports Medicine, the researchers say: "Conventional sports which incorporate many aspects of the broader society (for example, rules, regulations, authority figures) may appeal to the non-delinquent, but for the delinquent, who by definition 'violates the rules and norms of society', these activities offer little appeal."
They suggest the more adventurous, outward bound-type activities may provide a more attractive and effective means of helping the young delinquent.
And they stress their findings do not mean sporting activity should be discouraged "as there are many other good reasons why young people should engage in such activity".