Descriptions of social movement factionalism are often based on the dichotomous conception of lawful moderates and violent radicals. In this article, we nuance this distinction by illustrating the complexity of radical flanks through an empirically grounded analysis of protest tactics, in which we ask under what conditions radical flanks are likely to use violent protest tactics. Exploring dominant explanations of political violence, the article shows the necessity of understanding the use of violent protest tactics as part of cognitive and relational processes. The use of violent tactics varies greatly across frames and protest issues, pointing to how different logics of protest are tied to different frames. Also, the use of violence is affected by the presence or absence of moderate allies; the likelihood of violence clearly decreases when radicals and moderates form coalitions when organising protests. The analysis is based on a protest event data set covering over 3,900 nonviolent and violent events by the Radical Left-Libertarian Movement in Sweden, 1997-2016. Notably, the results hold over this entire twenty-year period, suggesting that they are robust and provide a better explanation than historically contingent causes.