Flag off Definition 1 of 2Pro Tip 1/3Event Initiation Used to describe the ceremonial action of starting an event, often by a dignitary or official. The mayor will flag off the annual parade. Pro Tip 2/3Specific Actions Typically involves a physical flag being waved to signal the start, especially in races. Watch for the moment they flag off the grand prix. Pro Tip 3/3Not General Use Reserved for formal event beginnings, not used for casual or informal starts. You wouldn't 'flag off' a friendly game of soccer.