In professional sumo, the referee’s war fan is called a gunbai.
A gunbai is a traditional Japanese military-style fan carried by the gyōji, the referee inside the ring. During a bout, the gyōji uses it to indicate the direction of the wrestler he judges to have won.
The fan is a visual part of the referee’s formal costume and authority. After the bout, the gyōji points the gunbai toward the winner, although a ringside judge can request a review if the decision appears questionable.
Gunbai is not the name of the wooden clappers used in tournament ceremonies, nor is it the name of a wrestler’s decorative apron. Those objects belong to different parts of sumo’s equipment and ritual vocabulary.