To fill the gap in theoretical and empirical knowledge on workplace aggression by teachers working in teams, this study explored its components, its targets, and its contextual determinants. Data were collected through three observations at different schools and at different times on 29 math, homeroom, language, and science studies teams. Qualitative analysis found the components of team teachers' aggression to include obstructionist behaviors and expressions of hostility to colleagues. Determinants of the aggression such as injustice and sense of workload were identified. Theoretical and practical implications for the educational system and educational research are suggested. Principals are strongly encouraged to establish a school environment that promotes justice and reduces work overload. Educational leaders should create workshops for teachers coping with the negative effects of aggression and implement dispute resolution systems. New directions for research on teachers' role in preventing aggression are offered.