This is also a play of the previously mentioned master who waits in posta dente di zenghiaro. In his place, I do this. When the lance is beaten aside, I turn my spear and strike with the butt, which is capped in well tempered steel.
Although the context is different, this play is essentially the same as the counter to the masters of spear on foot. You will notice it is also mechanically very similar to the pommel strike used by the 3rd scholar of the 3rd master of sword in two hands.
The master play has you waiting for your opponent in Posta Dente di Zenghiaro. As they bear down on you, step offline and beat up with your spear point, knocking your opponents lance past your head.
Depending on the individual circumstances of the beat, you may not be able to strike with the point as the 1st scholar suggests. If your spear point has risen too high, or your opponent is moving too fast, your opportunity to counter is not lost.
Step with your right foot to give yourself appropriate distancing. Given the motion of the horse, this will very probably be a step backwards. Continue the motion of the spear, rotating the butt upwards, directing it into your opponents face. You are in a mechanically strong position and your cover will push their lance aside. Their own momentum will cause them to impale themselves, as shown.
You will need to slide your hands on the spear shaft as it spins to give yourself the required reach. Notice the scholars left hand is in the middle of the spear, while their right is up by the spear head. You will also need to take care to give yourself enough space to be safely off to the side. Even if your counter is successful, if you are hit by your oppponents foot or knee as they pass, you can still potentially be knocked to the ground and trampled underfoot by the horse.