Translation
I am the counter of the fourteenth play, and any other that puts his hands on my face while grappling. I take my thumbs and I put them in his eyes if I find them uncovered. And if his face is covered, I take the elbow and grip or lock it immediately.
Interpretation
The text here draws attention to Fiores less than great naming conventions. He says this is the counter to the fourteenth play, by which he means the fourteenth not counting the master play. In other play counts throughout the book, he does include the master play, although not always. Regardless of what he calls it, he is clearly referring to the play immediately preceding this one. In a more standardised naming convention, this is the counter to the 12th scholar.
The scenario is that as the player to the 12th scholar, your opponent has gone for a low grab. You have countered this by grabbing at your opponents head with the intention of twisting them to the ground. As a response, your opponent is pushing back into your face, aiming to lever your head straight backwards, pushing you over.
Your hands are already almost in place to make the counter. Slide them around your opponents head slightly. Use the two bottom fingers of each hand to hook under the corner of the jaw. Your thumbs will naturally fall into your opponents eye sockets, and the corner of the jaw makes for a solid fulcrum to lever off.
Ideally, you are aiming to push your thumbs into the gap between the top of the eyeball and the socket. Get them right in to the knuckle. This will break the delicate bone on the floor of the socket, pushing the eyeball through, if not gouging it out completely. It is an unpleasant sensation for both parties. Although still very much alive, your opponent will be completely incapable of fighting, or doing very much at all. Regardless of someones strength, their eyes are extremely sensitive and vulnerable.
If your opponent is wearing a helmet, then making an eye gouge is impossible. Transition through the counter to the 4th scholar instead, and continue on with the 2nd scholar of the 3rd master of dagger.
You do this by pushing up on your opponents right elbow using your left hand. With your right hand, grab their left. Put your thumb on the back of the hand, and wrap your fingers over the ulnar edge. Twist the wrist and crank the elbow over, locking it. Pivot clockwise on your left foot, with your right foot arcing around behind you 180 degrees. This will free you from your opponents grip and allow you to spin them to the ground with the elbow lock.