If Fencer X, having received a yellow card, parries and then scores a valid touch, what should the referee do?

In this scenario, the correct response focuses on the implications of receiving a yellow card in the context of subsequent actions during a bout. A yellow card is issued as a warning for minor infractions or unsporting conduct, indicating that the fencer needs to correct their behavior. If Fencer X receives a yellow card and then subsequently scores a valid touch after performing a parry, the infraction still stands.

When a fencer has already been cautioned with a yellow card, any further indication of misconduct, even if accompanied by a valid action like scoring a touch, can result in an escalation of penalties. Therefore, in this case, after assessing X's actions following the yellow card, the referee correctly identifies that the appropriate response is to annul the scored touch and issue a red card for a subsequent offense, as a yellow card indicates repeated misconduct.

This means Fencer X’s misconduct led to a specific escalation in penalty, which is reflected in the issuance of a red card. In contrast, other options like allowing the touch or revoking the yellow card do not align with the rules governing the consequences of repeat offenses in fencing, where a yellow card indicates a warning and a further infraction can result in a more severe penalty.