American football positions have slowly evolved over the history of the sport. From its origins in early rugby football to the modern game, the names and roles of various positions have changed greatly, some positions no longer exist, and others have been created to fill new roles. Origins in rugby Being variants of 19th century rugby football, American and Canadian football position nomenclature has its origin there. Early rugby did no more than distinguish in tactics between the great bulk of the players who played as forwards and the relative few who played back defensively as "tends", as in goaltenders. After a while, the attacking or at least counterattacking possibilities of playing close behind the scrimmage (which later came to be called "scrummage") came to be recognized, and some players stationed themselves between the forwards and tends as "half-tends". It being seen that the players outside scrimmage (the "pack", i.e. the forwards) were not limited to a defensive role, the tends and half-tends were renamed "back" and "half back" positions. As the game became more sophisticated, backs positioned at different depths (i.e. distances behind the forwards) were further differentiated into half back, three quarters (the fraction 3/4) back, and full back, according to English and Scottish nomenclature, or quarter back, half back, and full back in the Irish nomenclature. In rugby the English-Scottish nomenclature was eventually adopted worldwide, with the word, "back", often omitted for brevity from the half back ("half") and three quarters back ("three quarter") names, and "fullback" as a single word. In some systems, "five-eighths back" was added. (The illustration here, of singular forms, should not be construed as indicating the number of players in any of those positions, nor is the fraction in the name at all proportional to the actual depth of the position; they indicate only a form of ordinal number, not cardinality.) Having the backs at different depths facilitates passing movements in which the ball is tossed from one player to (usually) the next closest, such that each back receiving the ball in turn can be running forward and yet not ahead of the player who threw it, since forward passing of the ball is illegal. Because of the involvement of the 3/4 backs, such a movement is often called a three-quarters movement. It was the Irish nomenclature of quarter back, half back, and full back that came to North America for use