The classification rules of the International Federation for Sitting Volleyball state that athletes with a physical impairment are eligible to compete in the sport at the Paralympics.
Classification also groups athletes in classes, defined by the degree to which they are limited in their ability to perform activities within that sport.
In Sitting Volleyball, there are two categories of classification: Disabled (D) and Minimally Disabled (MD). As these names suggest, D athletes have an impairment that has a greater impact on the field of play than MD players.
A number of players with the class MD played standing volleyball and picked up a significant injury to their ankle or knee, making them eligible to compete in Sitting Volleyball.
A maximum of one MD player may be on the court for each team at any one time.
Read an overview of classification at the London 2012 Paralympic Games