When should a fencing bout be stopped?

A fencing bout should be stopped when there is a safety issue or a clear rule infraction, as this is a critical aspect of maintaining the well-being of the fencers and the integrity of the competition. Safety is of utmost importance in fencing, where fast-paced, potentially dangerous actions occur. If a fencer appears to be in danger of injury due to improper conduct or if a violation of the rules could lead to an unsafe situation, the referee must intervene immediately. This ensures that the environment remains safe for all participants and upholds the standards of the sport.

The other choices do not prioritize the critical aspects of safety and fair play, which are foundational in officiating. A bout should not be stopped merely because one fencer is losing or if the crowd is disruptive, as these factors do not affect the immediate safety or legality of the bout. Stopping a bout solely at the end would ignore situations where an immediate intervention is necessary to avoid harm.