Why do lawmakers resort to physical violence in some parliaments but not in others? Brawls not only constitute a stark break with democratic norms and ideals, they also affect voter perceptions and have been seen as a bellwether for conflict and democratic backsliding. Yet, the phenomenon remains poorly understood. This paper introduces a new, original dataset recording reported incidents of physical fights in parliaments across the globe between 1980 and 2018 that includes almost four times more cases of violence than existing data. Theoretically, we argue that levels of democracy and the composition of parliament should drive violence. The analysis shows that fighting is most common in countries that are neither very autocratic nor very democratic, in fragmented parliaments, and in chambers with slim majorities. The findings have implications for the study of (de-)democratization, political instability, and the design of democratic institutions.