This play is very little used in the art of the dagger, but it is also a defence, and more for the scholar to learn. Beating the attack in such a way will hurt the player, namely with a counterstrike to the ribs or belly.
It is surprsing to see Fiore describe this play as being little used, because it is one of the simplest plays in the entire Fior di Battaglia.
As your opponent strikes, reach out toward them and catch the incoming attack with the palm of your left hand. Although described as a beat, it is perhaps more accurate to describe this as a brushing defence. You are not trying to either catch, grab or stop the attack. You are barely even redirecting it. For the most part, you are simply using your left hand to track your opponents dagger. Ensure that it stays to the right of your centreline.
Step with your front foot to the left, which will put you on the outside line. Your right hand is chambered to deliver a counterstrike. A number of options are available to you.
To mention just a few of the many directions you can take from this position, you could punch or strike with a dagger into the ribs or solar plexus as mentioned. You could just as easily counterstrike to the head.
Alternatively, you could grab your opponents wrist with your right hand, slide your left to their elbow, and spin them to the ground with an elbow lock, similar to the 2nd scholar of the 3rd master of dagger.
Equally, you could step through with a neck throw as described by the 3rd scholar of the 1st master of dagger.