Rugby is a game played with an oval shaped ball. There are fifteen players on each team. Teams attempt to advance the ball toward the in-goal area (similar to the endzones in football). In front of the in-goal areas there are goalposts similar to the field goal posts in American football which are used for scoring penalty kicks or drop goals. In rugby, the ball can only be passed backwards or sideways. Passing the ball forwards results in an infraction, as does inadvertently knocking the ball forward with the hands (known as a knock on). However, the ball can be kicked forward or advanced forward with any other part of the body. The defending team tries to gain possession back by tackling the player with the ball. Doing so will often force a ruck where the defending team can attempt to obtain possession of the ball.