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
Health issues in American football to field condition. Because American football is a full-contact sport, head injuries are relatively common. According to the San Francisco Spine Institute at Seton Medical Center in Daly City, California, up to 1.5 million young men participate in football annually, and there are an estimated 1.2 million football-related injuries per year. An estimated 51% of injuries occur during training sessions, while 49% occur elsewhere. Injuries are nearly 5 times more likely to happen during contact training sessions than in controlled, non-contact sessions. Older players are at the most risk for injuries, while teams with experienced coaches and more assistant coaches