The stop card in a bridge game is used when players use a bidding box. The bidding proceeds silently as each player pulls an appropriate card from the box and lays it on the table so all players can see it. Bidding boxes are generally used in tournament play or to play duplicate bridge. They may also be used if a player has a hearing disability. The stop card indicates your intention to make an unusual bid and prevents players from signalling non-verbal cues about their hands.
Announce your intention to skip at least one level beyond the most recent bid. All players require this critical information, but ACBL rules oblige you to ensure your left-hand opponent understands your intention.
Place the stop card on the table in a position that is easy for your left-hand opponent to see. When you play the stop card, the next player must pause before making her bid because your jump could cause her to hesitate and signal unauthorised information.
Choose the appropriate bid card and place it on the table. Put the stop card back in your bidding box after you complete your bid. If you forget to replace the card, you won't incur a penalty, according to the ACBL. However, if you play the stop card but then fail to make a skip bid, explain to the director how your use of the card was inadvertent rather than intentional.
Ask your director about stop card rules in your club. The language used by the ACBL leaves room for interpretation. Some clubs do not require the use of the stop card in duplicate play.
Maintain an undisturbed tempo in bidding and in your play of your hand. Hesitations while bidding or playing your cards could mean the director will judge against you and change your score.