In sports, a false start is a disallowed start, usually due to a movement by a participant before being signaled or otherwise permitted by the rules to start. Depending on the sport and the event, a false start can result in a penalty against the athlete's or team's field position, a warning that a subsequent false start will result in disqualification, or immediate disqualification of the athlete from further competition.

In gridiron football, a penalty is a sanction assessed against a team for a violation of the rules, called a foul. Officials initially signal penalties by tossing a bright yellow colored penalty flag onto the field toward or at the spot of a foul.