Flag football is a version of American football or Canadian football that is popular worldwide. The basic rules of the game are similar to those of the mainstream game (often called "tackle football" for contrast), but instead of tackling players to the ground, the defensive team must remove a flag or flag belt from the ball carrier ("deflagging") to end a down. In most organized play, players wear a belt. These belts vary from "Triple Threat" where the entire flag belt is removed, to "Sonic Pop" where only the flag is pulled.

Chiefly because there is no dominant sanctioning organization for the sport, the game has mutated into many variations: 9-man, 8-man, 7-man, 5-man, and 4-man on a side; with kicking and punting and without; with point-after conversions (including some with 1, 2, and 3 point tries) or without; and field sizes that vary from full CFL size, NFL size (120 yards long by 53 1/3 yards wide), to fields a third that size.

An important distinction is whether linemen are allowed to catch passes ("Eligible Linemen") or, as in the CFL / NFL, are not allowed to do so ("Ineligible Linemen"). Flag (and touch) football may also be divided into "contact" or "non-contact", depending on whether or not blocking is allowed; if allowed, blocking is usually restricted to the chest.