A lucky loser is a sports competitor (player or team) who loses a match in a knockout tournament or loses in qualifying, but who then enters the main draw. This can occur when another competitor withdraws during the tournament because of illness, injury, or other reasons, in which case the lucky loser re-enters the competition in place of the withdrawn competitor, or due to the structure of the tournament.
In the event of a lucky loser's re-entry to a competition, it usually occurs before all competitors in the main draw have started their first match in the tournament.