Sitting volleyball players must have part of the body between the buttocks and shoulders in contact with the court when a shot is made. Shuffling round on your backside is not easy. In goalball, blindfolded players aim a ball with a bell inside at their opponents’ net. I feel as if someone is going to trip me up. With only the vaguest sense of the heavy sphere heading in my direction — it can travel at up to 60mph — I lie down and hope it hits me, gasping when it thuds into my chest.