The present paper outlines a case study in sport psychology service delivery provided to a 16-year-old high school baseball player. The client reported experiencing distraction from overthinking in training and competition, which hindered his concentration and performance. An acceptance and commitment therapy intervention was implemented over 10 sessions across a 5-month period. The aim of the intervention was to overcome anxiety by encouraging acceptance of unhelpful thoughts, rather than changing or removing them, and helping the client focus on moving toward the athlete he wanted to be. This case offers a novel contribution to the wider literature by reporting an acceptance and commitment therapy intervention addressing performance anxiety in sport. We report how psychological flexibility was achieved through exercises to “unhook” the client from his thoughts around perfection and self-imposed pressure. Reflections from the client and practitioner capture the evaluation of the service delivery process.