In this paper we focus on the handling by the police of mass demonstrations in Switzerland during the past three decades. Our aim is to single out the determinants of police intervention during these protest events. We look at three sets of potential causes: (1) the configuration of power (i.e. political alliances and coalitions), (2) face-to-face interactions between protesters and the police during demonstrations, and (3) the broader public attention towards the protests. We test hypotheses regarding these three sets of causes using protest event data and applying both time-invariant methods and time-series analysis. The results show that (1) political alliances and coalitions do not have the impact that previous studies have predicted, (2) it is repression that causes violence rather than the other way around, and (3) the likelihood and modes of police intervention are influenced by the broader public attention given to ongoing protests.