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
Uniform number (American football) determining possible rules infractions by players. Under current rules in all three of the most prominent levels of American football (high school football, college football and professional football), all players must wear a number from 1 to 99, and no two players on the same team may wear the same number on the field at the same time. In the past, players have used the numbers 0, 00 and, in two special cases, 100. Those who wear numbers from 50 to 79 are, by rule, playing in specific positions which are prohibited from catching or touching forward passes if their