The first example of the guard used by the blue fencer can be found in Marozzo. Steven Reich’s Comparison of Guards from the 1536 and 1568 Editions simply lists this as “Guardia Unknown”.
At first I thought this was a variant of Meyer’s Longpoint. Also known as Langort, this is a transitional guard that one usually passes through when moving from one guard to another via a cut. It is called out because at this point one can choose to either turn the cut into a thrust or complete it by passing into one of several guards. Beyond this point one is pretty much committed.
The caption for Talhoffer reads:
The one on the left cuts from above. The one on the right cuts from below.
This is a bit hard to understand because it looks more like the one on the right has already completed a cut from below. Then I saw this:
This is Fiore’s Posta do Bicorno with an interpretation by Jim Barrows. This awkward looking pose allows one to make long-edge cuts from below to attack the face and arms.
An interesting feature of this guard is that is can absorb and redirect the momentum of a high cut. Imagine if you will that someone in vom Tag were to cut at someone in Langort. The blade in Langort would be driven into the ground and its owner would find himself with a sword in his chest or face.
Now repeat the experiment with vom Tag and Bicorno. Instead of being driven directly into the ground, the blade in Bicorno want to travel in a circular path. This path concludes with a downward cut to the forehead of the opponent.
The unusual guard Talhoffer is showing is Bicorno, a guard used specifically used to counter high cuts such as those thrown from vom Tag.