A4 is an amputee sport classification used by the International Sports Organization for the Disabled (ISOD).for people with acquired or congenital amputations. People in this class have one leg amputated below the knee. Their amputations impact their sport performance, including having balance issues, increased energy costs, higher rates of oxygen consumption, and issues with their gait. Sports people in this class are eligible to participate in include athletics, swimming, sitting volleyball, archery, weightlifting, wheelchair basketball, amputee basketball, amputee football, lawn bowls, and sitzball.