An end in American and Canadian football is a player who lines up at either end of the line of scrimmage, usually beside the tackles. Rules state that a legal offensive formation must always consist of seven players on the line of scrimmage and that the player on the end of the line constitutes an eligible receiver. Before the advent of two platoons, in which teams fielded distinct defensive and offensive units, players that lined up on the ends of the line on both offense and defense were referred to simply as "ends". The position was used in this sense until roughly the 1960s.