This study aimed to analyze and interpret children’s utterances in the classroom, as well as when they moved around during games of flag football. We used this case to clarify the ways in which children make decisions in this context. We derived the following four points: (1) It was possible to ascertain how children on the defense team in the game engaged in decision-making with respect to the sampling group, based on an analysis of the teacher’s guidance and the children’s utterances and movements in class. (2) The children made decisions based on the knowledge they had acquired through learning. (3) The children were able to make decisions and respond immediately to offensive maneuvers that differed from the ones they had initially anticipated. (4) The children had the knowledge they needed for decision-making and were able to make decisions, but this was not always consistent with their actions.