The present case study illustrates the treatment of a 19-year-old female lacrosse player, classified as experiencing Performance Dysfunction (Pdy) by the Multilevel Classification System for Sport Psychology (MCS-SP). The self-referred collegiate athlete was treated using the manualized Mindfulness-Acceptance-Commitment (MAC) protocol (Gardner & Moore, 2004a, 2007). The intervention consisted of eight individual sessions and several follow-up contacts via e-mail. The majority of the sessions addressed clinically related and sport-related concerns, including difficulties in emotion regulation and problematic interpersonal relationships. Based on self-report, coach report, and one outcome assessment measure, the psychological intervention resulted in enhanced overall behavioral functioning and enhanced athletic performance. This case study suggests that following careful case formulation based on appropriate assessment and interview data, the MAC intervention successfully targeted the clearly defined psychological processes underlying the athlete’s performance concerns and personal obstacles, thus resulting in enhanced well-being and athletic performance improvements.