American flag football is a popular sport originated from the National Football League (NFL), which introduces the basic rules and techniques of American football to teenagers aged 8-/kloc-0-4 all over the world. Compared with formal football, flag football is not allowed to hug and push people. The attack stopped when the defender pulled down the flag on the belt of the attacker with the ball. It is a safe "non-collision" sport, which is popular among teenagers in more than 30 countries around the world.