Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A rugby league team consists of thirteen players on the field, with four substitutes on the bench. Players are divided into two general categories: "forwards" and "backs". Forwards are generally chosen for their size and strength. They are expected to run with the ball and attack, and to make many tackles. Forwards are often required to do a lot of hard work such as making openings for the backs and gaining metres in field position. Backs are usually smaller and faster, though a big player who can run can be of advantage in the backs. Their roles require speed and ball-playing skills, rather than just strength, to take advantage of the field position gained by the forwards.