Aggression is strongly influenced by the surrounding socio-physical context, and the development of aggressive behavior is best understood through a continuous cycle of ongoing person-environment interactions. Empirical studies, nevertheless, have been predominantly conducted in the laboratory, studying aggression as a short-lived phenomenon, emerging from and within an individual, and – with situational factors studied in isolation – devoid of its context. The present field study, conducted in an urban nightlife area, complements this research. A qualitative, multi-method approach was followed by thematic analysis to investigate ongoing behavioral patterns of the crowd vis-à-vis the changes in the context that co-occurred with the development of unwanted behaviors, including aggression. In our study, we identified atmosphere as a dynamic and mood-like, but extra-individual state of the socio-physical setting related to the development of aggression. Our results suggest that atmosphere affects the behavior of groups and individuals by emerging from and feeding into ongoing interactions between people and the environment. At the individual level, it appears to play its part as proximate determinant of behavior; at the crowd level it reflects the synergetic product of all those persons’ states, behaviors and interactions. Implications for aggression theory and for applications aimed at curbing aggression are discussed.