The aim of this pilot study was to examine the possible effects of a forum theatre intervention on moral team atmosphere, moral reasoning, fair play attitude and on- and off-field antisocial and prosocial behaviour in male adolescent soccer players from 10 to 18 years of age (n = 99). From pre-test to post-test, small but positive changes were found in moral atmosphere, but not in moral reasoning or fair play attitude. Changes were also found in on-field antisocial behaviour, which showed a significant decrease one month after the intervention. However, the changes in antisocial behaviour were not affected by the changes in moral team atmosphere. Off-field antisocial behaviour and both on- and off-field prosocial behaviour did not show a significant change. The results suggest that more extended efforts built on a similar approach are worth investigating. (Contains 1 table.)