Self-determination theory (SDT) has served as a theoretical framework for considerable research on teaching behavior and student motivation. The majority of studies have focused on need-supportive teaching behavior at the expense of need-thwarting teaching behavior (i.e., the "dark side" of teaching). The goal of the present study was to examine motivational dynamics involved in controlling teaching behavior in the context of physical education (PE). The majority of studies on observed teaching behavior were conducted in the laboratory. To augment the ecological validity in the present study, the behavior of PE teachers was videotaped to rate their controlling teaching behavior in a real-life setting. In a sample of 56 teachers and 702 secondary school students, controlling teaching behavior during a specific PE class, as observed by external raters, was related positively to students' perceived controlling teaching behavior and, through these perceptions, to controlled motivation and amotivation. These associations were obtained in spite of the low incidence of controlling teaching behaviors, suggesting that students may be quite sensitive to controlling teaching behaviors. No associations were found between observed controlling behavior and student autonomous motivation and students' perceptions of autonomy-supportive teaching. Practical implications and recommendations for PE teachers' professional development training are included.