Comparison of American football and rugby union

A comparison of American football and rugby union is possible because of the games' shared origins, despite their dissimilarities.

In the event of a tackle in rugby the player may pass the ball behind him provided he is not on the ground. If the tackled player is on the ground, the ball must be released, allowing any other player (including the opposition) to pick up the ball (usually a ruck forms) and the play continues. In the event of a tackle in American Football the play is concluded and the team on offense maintains possession usually if either the ball was advanced past the first down marker (resulting in a first down and a renewal of the down count) or else the down count advances (although if the play was the fourth down play and the ball is not advanced past the first down marker then the defensive team would gain possession).

In rugby union, it is against the rules to throw (pass) the ball in a forward direction: a player in a position to receive such a pass would in most cases be offside anyway. In American football, a player behind the line of scrimmage (most often the quarterback) is permitted to throw the ball forward from behind the line of scrimmage, provided that only one forward pass may be attempted during each play. A player can attempt a forward pass if he has already received a backwards pass, provided he stays behind the line of scrimmage.

Professional and most scholastic American football team play has evolved from a single team with all players except limited substitutions playing the entire game, to a specialized "platoon" system consisting of three separate units (offensive, defensive, and "special teams" used for kicking and punting) with only one of the three being on the field at a time. That is to say that in professional American football, the majority of players play in only one specialization (or "one side of the ball") – however, every player is eligible to play in any specialization.

In rugby the teams are divided into eight forwards and seven backs. Both groups of players partake in attacking and defensive plays and are on the pitch at the same time. Only the eight forwards take part in the "set pieces", which are ways to contest ball possession when there is a minor rule infringement or the ball passes out of bounds. These set pieces are scrums, tests of strength, and line outs. A person's build and skill set determines which group they can play in. All forwards must be heavy and strong to scrummage well but not so heavy that they are too slow to partake in attacking plays. The backs are lighter and faster and include the expert kickers. The forwards numbered 1 to 8 are the players that need to have good all-round rugby skills as well as speed and strength. In professional rugby there are very few players who can play equally well in a variety of positions and most will play in the same position from youth.

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