NFL teams rarely recruit players from other gridiron football leagues. A touchdown is a scoring play in gridiron football. Arena football is a variety of eight-man gridiron football. Tackle is a playing position in gridiron football. Starting play from the line of scrimmage in gridiron football is derived from the scrum. The two sports are considered the primary variants of gridiron football. The football helmet is a piece of protective equipment used mainly in gridiron football. These risks come from running, basketball, association football, volleyball, gridiron, gymnastics, and ice hockey. A kickoff is a method of starting a drive in gridiron football. A down is a period in which a play transpires in gridiron football. In Canada and the United States, rugby developed into gridiron football. Defensive end (DE) is a defensive position in the sport of gridiron football. Lincoln varsity sports games were also televised on City Gridiron. A running back (RB) is a member of the offensive backfield in gridiron football. A linebacker (LB or backer) is a playing position in gridiron football.