A "red card" is a disciplinary tool used in sports, particularly in soccer, to indicate that a player has committed a serious foul or misconduct. When a referee shows a red card, the player must leave the field immediately and cannot be replaced, leaving their team with one fewer player. This action is meant to maintain fair play and ensure the safety of all participants. In addition to soccer, red cards are also used in other sports, such as rugby and hockey, to penalize players for severe infractions. The rules surrounding red cards vary by sport, but the primary purpose remains the same: to uphold the integrity of the game and discourage dangerous behavior.