A defensive specialist in volleyball is a player who can substitute for any other player. The defensive specialist can play any position on the court but typically substitutes for back-row players.
Volleyball is a team sport that is played with a net between two teams of six players each. Teams attempt to score points by hitting the ball to the ground on the other team's side of the net. The sport became part of the Summer Olympic Games in 1964.
Volleyball was first played in 1895 when a physical education director at a Massachusetts YMCA created a game called Mintonette. The game was played indoors, and any number of players could participate. It was designed to be more gentle than basketball and suitable for older YMCA members.