In several forms of football, a forward pass is the throwing of the ball in the direction in which the offensive team is trying to move, towards the defensive team's goal line. The legal and widespread use of the forward pass distinguishes gridiron football (American football and Canadian football) from rugby football (union and league) from which the gridiron code evolved, in which the play is illegal.
Illegal and experimental forward passes had been attempted as early as 1876, but the first legal forward pass in American football took place in 1906, after a change in the rules. Another rule change on January 18, 1951, established that no center or guard could receive a forward pass, and a tackle may only do so if he announces his intent to the referee beforehand that he will be an eligible receiver, called a tackle-eligible play. The only linemen who can receive a forward pass are the ends (tight ends and wide receivers). The rules regulate who may throw and who may receive a forward pass, and under what circumstances, as well as how the defensive team may try to prevent a pass from being completed. The primary passer is the quarterback, and statistical analysis is used to determine a quarterback's success rate at passing in various situations, as well as a team's overall success at the passing game.