Teamwork is a central tenet of agile software development but various teamwork theories only partially explain teamwork in that context. Big Five teamwork theory is one of the most influential teamwork theories, but prior research shows that the team leadership concept in this theory it is not applicable to agile software development. This paper applies an adapted form of Big Five teamwork theory to cases of agile software development. Three independent cases were drawn from a single organisation providing a measure of control over contextual factors affecting the teamwork. The findings show that the adapted form of Big Five teamwork theory, including a shared team leadership concept, is fully applicable to some forms of agile software development, but not all. For practitioners, insights as to which agile practices support teamwork are provided.