Riposte in Quatra Over the Arm (Plate 53)
Commentary
Jonathan Allen
This variant combines the main sequence with the 2nd play where you drive down the opponent's sword in Quarta so you can thrust under their right arm (Plate 53).
It is important to be in Quarta by the time you finish the disengage. If you disengage in Tertia, you'll be forced to try to mutate into Quarta while covering their blade. This will likely end with you getting tangled up and you'll lose the opening.
Another way of saying this is that you press down on their blade in Quarta, not in Tertia.