Swimming is a fundamental sport at the Olympic and Paralympic games, with the Paralympic classification system being the key difference between these games. To improve the accuracy of the classification system this case study investigated differences in the underwater hand kinematics of the affected and unaffected limb of an elite Para swimmer with hemiplegic cerebral palsy. In this case study, hemiplegic cerebral palsy caused impairments in strength, motor coordination and range of motion that affected hand speeds and trajectory paths during the underwater stroke phases. This work illustrates the benefit of using objective impairment and sport-specific measurements to gain insights into the impact that health conditions have on performance to guide Para swimming classification. This biomechanical analysis lays the foundations for the future improvement in international Para classification system