What action should the Referee take when Fencer X makes a valid riposte after retreating behind the end line?

In fencing, when a fencer retreats behind the end line, they are considered to be leaving the valid area of play. This is an important rule, as the boundaries of the fencing strip define where valid actions can take place. If Fencer X completes a valid riposte while behind the end line, despite the action being valid in a different context, the critical factor is that they have effectively left the playing area when executing the move.

As a result, because Fencer X is out of the bounds of the strip when making the riposte, their action does not count. The referee has to acknowledge that Fencer X was not in a position to score a valid touch due to their illegal status outside the fencing area. Therefore, since Fencer Y is still within the valid area and the natural consequence of any action taken by Fencer X (who is out of bounds) leads to Fencer Y being awarded the touch.

Thus, the correct action for the referee in this situation is to award a touch to Fencer Y, as the actions of Fencer X do not hold validity while outside the established boundaries of the fencing strip.