This article is from the Table Tennis (Ping Pong) FAQ, by ttennis@bu.edu with numerous contributions by others.
21.1 All rules in this section shall apply only to Wheelchair
competition.
21.2 All competitors shall compete in wheelchairs.
21.2.1 Each wheelchair shall conform to the dimensions stated in article
III of the Constitution and Bylaws of the National Wheelchair
Athletic Association (N.W.A.A).
21.2.2 A cushion, of any size and made of any foam rubber, may be used.
21.2.3 The wheelchair is not required to have back support.
21.3 Wheelchair competitions may be divided into up to four divisions.
These divisions shall be based on the N.W.A.A. classification
system, as follows:
21.3.1 Division 1: all wheelchair players classes I through V.
Division 2: classes I through III
Division 3: classes IA, IB, and IC
Division 4: class IA only.
21.4 Each division shall have either 1.) both men's event and women's
event, or 2.) an open event. If any division does not have a
women's event, or if the women's event is cancelled, the women
entered in that division will be allowed to compete with the men in
what becomes the open event in that division.
21.5 The table not have any physical barrier that can in any way hinder
the normal and legal movement of the competitor's wheelchair.
21.6 In service, the receiver is required to make a good return.
However, if the receiver does not strike or obstruct the service,
and the served ball does not continue, under its own momentum, to
leave the table by crossing the receiver's endline, the rally shall
be a let.
21.6.1 In service, players classified as IA, IB or IC may project the ball
upwards with either hand.
21.7 Players classified as IA, IB or IC may touch the playing surface
with the free hand during play without losing the point; however,
they may not use the free hand on the table for support while
striking the ball.
21.8 In any match that includes at least one player classed as IA, IB or
IC, all players may volley the ball after it has crossed the
volleyer's endline or sideline without losing the point.
21.9 The competitor's feet may not touch the floor during play.
21.10 Competitors may not rise noticeably off their cushions during play.
 
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