H9: Over reaching (Überlauffen)
"Mark, that is when you come to him with the prefencing:
if he then hews below to your lower opening, do not
parry that, but hew in above strongly to his head. Or, if he
hews to you with Lower-hewing, then mark before he comes
up with the Lower-hew, and shoot the long point above into
his face or his breast, and Set-on him above so he may not
reach you below (since all upper Settings-on break and defeat
the lower)..."
Überlauffen is a concept created out of the geometry inherent in sword strikes. As your arms hang from the shoulder, the shortest line between you and a target on your opponent is generally a line straight from your shoulder, parallel to the ground extending towards them. If someone cuts to a low target, you may take advantage with a simultaneous strike of longer distance by aiming for an upper target.
A short video explaining the concept of Überlauffen may be found here.