In
soccer/
football, a warning given out by the
referee to a player for a clearly dangerous or intentionally extra-
legal play. The player's name and number are written in the game
book by the referee (hence the phrase "being
booked"), and an approximately 3" x 4"
yellow plastic card is displayed above the referee's head, with the referee facing in the direction of the player being carded.
A player may continue playing after receiving one yellow card; a second yellow card within a single match invokes an automatic red card, meaning ejection. In some leagues, an accumulation of a certain number of yellow cards over a given number of matches can result in suspension for future matches, even if no red was received in any particular match.