Flags flown on a beach.
Because of their ease of signalling and identification, flags are often used in sports.

>> In American and Canadian football, referees use flags to indicate an error has been made in game play. The phrase used for such an indication is flag on the play. The flag itself is a small, weighted handkerchief, tossed on the field at the approximate point of the infraction; the intent is usually to sort out the details after the current play from scrimmage has concluded. In American football, the flag is usually yellow; in Canadian football, it is usually red.

>> In auto and motorcycle racing, racing flags are used to communicate with drivers. Most famously, a checkered flag of black and white indicates the end of the race, and victory for the leader. A yellow flag is used to indicate caution requiring slow speed and a red flag requires racers to stop immediately. A black flag is used to indicate penalties.

>> In Association football (soccer), linesmen carry small flags along the touch lines. They use the flags to indicate to the referee potential infringements of the laws, or who is entitled to possession of the ball that has gone out of the field of play, or, most famously, raise the flag overhead to indicate an offside offence. Officials called touch judges use flags for similar purposes in both codes of rugby.

>> In addition, fans of almost all sports wave flags in the stands to indicate their support for the participants. Many sports teams have their own flags, and, in individual sports, fans will indicate their support for a player by waving the flag of his or her home country.

>> Capture the flag is a popular children's sport.