What is a unique requirement for athletes when playing Sitting Volleyball?

In Sitting Volleyball, a unique requirement for athletes is that they must maintain contact between their torso and the floor. This rule ensures that players remain seated while playing, which is fundamental to the game itself. By having their torso in contact with the floor, players can effectively engage with the game while respecting the sport's adapted rules. This requirement not only emphasizes the sitting nature of the sport, which distinguishes it from traditional volleyball, but also promotes fair play and ensures that all athletes compete under the same conditions.

The other options do not align with the essential rules of Sitting Volleyball. Athletes are not required to stand or use only one hand, nor do they need to wear special shoes to participate. The focus is on the seated position and maintaining contact with the floor, which is central to the integrity and safety of the sport.