American football is an exciting sport played by to two teams of 11 players, although up to 40 men can play for each team during a single match. The tactics of the game can be very complicated, but the object simple - to score points by crossing the opponents' goal-line with the ball (a "touchdown") or by kicking the ball between their goalposts. The game is therefore based around the teams' attempts to gain ground up the field. It was first played in the American colleges in the late 19th century and is, without doubt, the team sport with the greatest amount of physical contact. The helmets and huge shoulder pads worn by the players help make this one of the most spectacular of all sports. Canadian football has slightly different rules.