A rugby league football team consists of thirteen players on the field, with four substitutes on the bench. Each of the thirteen players is assigned a position based on both the role they are expected to fill within the team and the area they typically occupy on the field. These positions are defined by number and are standardised across all teams and matches, however the same rules apply equally to all players regardless of position and the positions are fluid, meaning players free to interchange between positions or take up a different position at any time. In practice, the positions simply serve as a guideline as to the player's expected role in both attack and defence.