American football American football American football, referred to as football in the United States and Canada and also known as gridiron, is a team sport played by two teams of eleven players on a rectangular field with goalposts at each end. The offense, which is the team controlling the oval-shaped football, attempts to advance down the field by running with or passing the ball, while the defense, which is the team without control of the ball, aims to stop the offense's advance and aims to take control of the ball for themselves. The offense must advance at least ten yards in four
Comparison of American football and rugby union front-row forwards). Rugby teams may make up to seven substitutions. Each team must field 15 players at the start of each match. Players who are bleeding may receive medical treatment off pitch and are replaced until they have stopped bleeding. If the bleeding has not stopped after 15 minutes of "real time", the player will be permanently substituted. This can be down to officials' discretion, depending at which level the sport is played, where only minor medical assistance is needed to make the player fit to return to the field of play. Ejected players in American football can be replaced