This article reports on a study of one recently qualified teacher’s employment of the Teaching Games for Understanding (TGfU) model in a UK secondary school. The study sought to examine how the teacher, not formally educated in its use, delivered TGfU and to identify those factors that led to this interpretation of the model. Occupational socialization was used to explore how childhood experiences of physical education (PE) and sport, higher education and the workplace influenced the experience of learning informally to use the model. Qualitative data are reported from interviews, lesson observations and teacher documentary evidence. Findings illustrated that informal learning during organizational socialization had developed the teacher’s use of TGfU. However, a partial understanding of the tactical problem-solving nature of games and issues around the use of social constructivist learning strategies impeded effective use of the model. It is recommended that teachers attempting to learn informally how to use TGfU effectively receive sustained external expertise and continuing support from colleagues.