In recent years there has been a growing interest in Urban Screen applications. While there have been several deployments of these technologies in our urban environments, surprisingly little research effort has aimed to explore the detailed material practice of people's engagement and interaction with these urban screen applications. In this paper, we present a study of collaborative game play on large urban displays situated in three city locations in the UK. The study highlights ways in which collaborative play is initiated and coordinated within the context of an urban environment. These experiences are related to physical characteristics of the architectural spaces, the people populating these spaces and the interactive properties of the game itself. The study moves on to discuss issues relating to audience and spectatorship, an inherent feature of interaction in urban environments. The issues of audience and spectatorship are discussed in their own right but also in terms of their relationship to the playing experience. Finally the study considers these interactive experiences in the contexts of being hosted by a professional compere and also with no host present. Through the study we highlight factors to consider in the design of collaborative urban screen applications.