Gridiron football, or North American football, is football primarily played in the United States and Canada. The predominant forms of gridiron football are American football and Canadian football. Gridiron refers to the sport's characteristic playing field, which is marked with a series of parallel lines resembling a gridiron.
"Gridiron" football developed in the late 19th century out of the older games related to the games now known as rugby football and association football. It is distinguished from other football codes by its use of helmets and shoulder pads, the forward pass, the system of downs, a line of scrimmage, more specialist positions and formations, free substitution, platooning of different players for offense and defense, measurements in yards, a distinctive brown leather ball in the shape of a prolate spheroid, and the ability to score points while not in possession of the ball by way of the safety. Walter Camp is credited with creating many of the rules that differentiate gridiron football from its older counterparts.
In American football a play is a close to the ground "plan of action" or "strategy" used to move the ball down the field. A play occurs at either the snap from the center or at kickoff. Most commonly plays occur at the snap during a down. These plays vary between basic to very complicated. Football players keep a record of these plays in their playbook.
In sports, out of bounds (or out-of-bounds) refers to being outside the playing boundaries of the field. Due to the chaotic nature of play, it is normal in many sports for players and/or the ball to go out of bounds frequently during a game. The legality of going out of bounds (intentionally or not), and the ease of prevention, vary by sport. In some cases, players may intentionally go or send the ball out of bounds when it is to their advantage.
In several forms of football a forward pass is a throwing of the ball in the direction that the offensive team is trying to move, towards the defensive team's goal line. The forward pass is one of main distinguishers between gridiron football (American football and Canadian football) in which the play is legal and widespread, and rugby football (union and league) from which the North American games evolved, in which the play is illegal.
In some football codes, such as association football (soccer), the kicked forward pass is used so ubiquitously that it is not thought of as a distinct kind of play at all. In these sports, the concept of offside is used to regulate who can be in front of the play or be nearest to the goal. However, this has not always been the case. Some earlier incarnations of football allowed unlimited forward passing, while others had strict offside rules similar to rugby.
In the National Football League, an illegal procedure can be used to refer to one or any number of a set of penalties. It is not itself a particular penalty, but an encompassing term which can describe several infractions.
In many cases, most notably in the National Football League, this type of penalty has even been given its own signals. Examples of this include: