During play, a team consists of six players: a goaltender and five "runners". A runner is any non-goalkeeper position player, including forwards, transition players, and defenders. Runners usually specialize in one of these roles and substitute off the field when the ball moves from one end to the other. When the sport originated teams played with six runners. However, in 1953 the sixth runner, a position called rover, was eliminated. The goalkeeper can be replaced by another runner, often when a delayed penalty has been called on the other team or at the end of games by teams that are behind to help score goals.