Research on deradicalization and disengagement from terrorist groups has produced insights into factors motivating to turn to violent milieus as well as reasons for turning away from them. Less exploration has focused on the group dynamics involved when individuals leave the group. In particular, the social pressure component, including the use of retaliatory violence, has not been adequately addressed. Testing Levine and Moreland’s theoretic model of group reaction to disloyalty, this article illustrates how extremist groups determine the type of social pressure, using five problem-centred interviews with former German neo Nazis, as well as 12 cases of violent social pressure on defectors in Germany and the United States. The main argument of this article is that a group’s internal negotiation process regarding the pressure is typically segmented into two phases: one emotionally-based, immediately after the defection and a second, more rational and strategic response phase later on. Important factors determining the group’s reaction are: the in-group status of the defector, group specific ideology, in-group future prospects and strategies, group structure, prevention of further defection, in-group behavioural learning processes, the defection process itself, and pressure on the group from the government.