I have found some more information here: http://www.itfwheelchairtennis.com/a...ligibility.asp
QUAD ELIGIBILITY RULES
The Competitive Wheelchair Tennis Player
i. In order to be eligible to compete in ITF sanctioned wheelchair tennis tournaments and the Paralympic Games, a player must have a medically diagnosed permanent mobility related physical disability. This permanent physical disability must result in a substantial loss of function in one or both lower extremities. Players must meet one of the following minimum eligibility criteria:
1. A neurological deficit at the S1 level or rostral, associated with loss of motor function, or;
2. Ankylosis and/or severe arthrosis and/or joint replacement of the hip, knee or upper ankle joints, or;
3. Amputation of any lower extremity joint rostral to the metatarsophalangeal joint, or;
4. A player with functional disabilities in one or both lower extremities equivalent to 1, 2 or 3 above.
ii. A quad player must meet the criteria for permanent physical disability as defined above. In addition, the player must have a permanent physical disability that results in a substantial loss of function in one or both upper extremities. Quad players must meet one of the following minimum eligibility criteria:
1. A neurological deficit at the C8 level or rostral, with associated loss of motor function, or;
2. Upper extremity amputation, or;
3. Upper extremity phocomelia, or;
4. Upper extremity myopathy or muscular dystrophy, or;
5. A player with other medical diagnosis resulting in functional disabilities in one or both upper extremities equivalent to 1, 2, 3 or 4 above.
iii. In addition, a quad player must have at least one of the four following functional disabilities with regards to upper extremity use, irrespective of trunk balance:
1. Lack of capacity to perform a smooth and continuous overhead service, or;
2. Lack of capacity to perform a smooth and continuous forehand and backhand, or;
3. Lack of capacity to manoeuvre a manual wheelchair using full wheel control, or;
4. Lack of capacity during play to grip the racquet for all strokes without taping and/or an assistive device.
Quad players must have a minimum of three affected extremities with a permanent physical disability as defined above, and at least one upper extremity must have a functional disability as defined above. Quad players may not use either foot to propel a wheelchair.