The article outlines a methodology for systematically observing collective violence (and public order policing in relation to it). Specific attention is given to matters of sampling and measurement and to the way in which observational challenges have been met in comparison with participant observational studies of demonstrations and football matches. The article shows that it is possible to conduct meaningful systematic observations of episodes of collective violence in a reliable way (more complete and more detailed than police records or newspaper reports) without compromising the physical safety of the observer. Even though violence at these types of events is relatively rare, it is also possible specifically to sample events with an increased likelihood for collective violence. Direct systematic observation of collective violence yields data that cannot be obtained by other means (surveys, interviews, participant observation) and that are crucial to an understanding of the initiation and escalation of collective violence.