Flag football is a version of Canadian football or American 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” which the entire flag belt is removed, to “Sonic Pop” which 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.
In Non-Contact flag football, there is no blocking, usually no linemen, and if there are linemen they can not use their hands to block an opponent. Defensive players cannot get in the way of a runner; they can only attempt to grab the flag without impeding the path of the runner. Offensive players are not allowed to hand block defensive players to prevent them from grabbing the flag.
In Contact flag football, none of the rules above apply. There are linemen blocking only around chest area, no chop blocks or blocks below the waist. Defensive players can get in the path of an offensive player to attempt to grab the flag.
Reference: Wikipedia Flag Football