A yellow card is a warning given to players in sports, particularly in soccer and rugby. It indicates that a player has committed a foul or unsportsmanlike behavior. If a player receives two yellow cards in a single match, it results in a red card, leading to their expulsion from the game. The purpose of the yellow card is to maintain fair play and discipline during the match. Referees use it to communicate to players that their actions are unacceptable. Accumulating yellow cards over multiple games can also lead to suspensions, affecting a player's availability for future matches.