What rule must referees adhere to regarding coaching during bouts?

Coaching is strictly prohibited during bouts to maintain the integrity of the competition and ensure that the fencers can perform independently without external influence. This rule is crucial because it prevents any advantages that might be gained from real-time instructions, allowing fencers to rely solely on their training, skills, and tactics during the match. By eliminating coaching during the bout, the referee helps to create a fair environment where the outcome is based solely on the fencers' abilities.

The prohibition against coaching is also vital for upholding sportsmanship and the spirit of the competition. It reinforces the concept that each match is a test of the individual fencer's preparation and strategy, rather than a team effort, which is particularly significant in individual sports like fencing.

In contrast, other options suggest scenarios where coaching might be allowed, which could undermine the rules of fair play and lead to confusion and inconsistency during the bouts. For example, allowing coaching during breaks could disrupt the flow of competition and potentially influence the bout in ways that are not intended by the rules.