The present case study aimed to clarify factors affecting the resumption of play in a sandbox by a 4-year-old boy who had instigated conflicts with his friends. We video recorded the play of a number of 4-year-old children in the sandbox. We focused on “boy A” who initiated conflicts with his friends, and then resumed playing with them. Analysis of his behavior using Trajectory Equifinality Modeling (TEM) revealed that two important factors were involved. Boy A acquired a tool and then established a role according to requests from his friends. He then became involved once again with a friend who gave a purpose and a role to his play.