Longman Dictionary of Contemporary English
Wiktionary
n. A version of American football where the players must remove a flag, worn around the waist, from the ball carrier instead of tackle.
Wikipedia
Flag football is a version of US-American football or Canadian football where 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.
Usage examples of "flag football".
You'll have two hours in the yard afternoons from four until six, except on Saturdays when the rest of the prison population has their flag football games.
The Black Mountain Police arrived with me before Whit appeared, and I sat in a cruiser parked on a dirt road, watching children play flag football.
A few neighborhood kids who were playing flag football in spite of the miserable weather stopped to gawk wide-eyed at the real-life police chase roaring up the suburban street.
He liked to play flag football on Sundays, had no drinking, gambling, or illegals problem.
He'd smile and nod and, avoiding the subjects of murder, rape and the Secret Service, talk only about what he saw in front of him: sparrows bathing in spring dust, trees, children playing flag football.
Or the Flag Football experience, where pages are plucked from the butts of the rival team.