This study explores behavioural determinants of defending behaviour in cyberbullying incidents. Three focus groups were conducted with youngsters aged 12–16y. Major themes that were found as important behavioural determinants to defend the victim were a low moral disengagement, that the victim is an in-group member and that the bystander is popular. Bystanders preferred to handle cyberbullying offline and in person, and comforting the victim was considered more feasible than facing the bully. With a high peer acceptance of passive bystanding and lack of parental support for defending behaviour, youngsters do not receive much encouragement from their environment to exhibit defending behaviour towards victims. These preliminary results suggest befriending and peer support interventions hold promise, as well as environmental interventions with parents and teachers. These first results will need to be confirmed in more in-depth analyses and in quantitative research.