What is the fine-grained topic of the following text: As for the red and yellow whistles, I preferred not to use them - sometimes as an AR I've heard the confusion that a glimpse of red or yellow can cause on the sideline, even had people start shouting out when the referee calls a player over, thinking the card is in the referee's hand when it's just the whistle! Only return the topic.
Experience and issues with using red and yellow whistles in refereeing football (soccer) matches