Comparison of American football and rugby union possession of the ball at their own 20-yard (25 yard line in College Football) line. An important difference between the two sports involves the aftermath of a score. In American football, the scoring team kicks off, except after a safety. In rugby union, the team conceding the score kicks off (in rugby sevens, a variant of rugby union featuring seven players per side, the scoring team kicks off). An American football team consists of an offensive unit, a defensive unit and a "special teams" unit (involved in kicking and kick returns). Only eleven players can be on the field at
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