From Longman Dictionary of Contemporary Englishyellow cardˌyellow ˈcard noun [countable] DSFa yellow card held up by a football referee to show that a player has done something wrong → red card
Examples from the Corpus
yellow card• As he came on, Rocky got a great reception from the crowd and a yellow card from the referee.• The Boro skipper raced across the field to remonstrate with the official and was lucky to escape with just a yellow card.• Then Aunt Della took a folded yellow card out of the box.• And anyway, I ain't got my yellow card on me.• The offence merited the second yellow card that would have put Ferguson off the park.• He was fortunate to be shown only the yellow card.• Bent's jaw was broken in four places, and Penney was shown the yellow card. 