What action is required by the Referee when Fencer Y scores a valid touch during an ongoing bout?

When a referee observes that Fencer Y has scored a valid touch during a bout, the action required is to record the touch and continue the bout. This is essential for maintaining the flow of the match and ensuring that the score reflects the performance of the fencers accurately. The referee is responsible for keeping track of the score, and immediate recognition of the valid touch allows for consistent updating of the bout's progress.

Recordkeeping is critical, as it informs both fencers of the current state of the match, and it maintains the integrity of the competition. By choosing to continue the bout without unnecessary interruptions, the referee ensures that the momentum of the duel is not lost, which is important for both the fencers' performance and the spectators' experience.