This is the play of the previous master who is waiting with the ghiavarina against the horsemen in Posta Dente di Zenghiaro. In passing off the line and beating the attack aside I enter this play, and because I understand how to place it, I can strike him in the head with a cut or thrust, my ghiavarina moves so well.
The play of the 1st scholar is technically very simple, although rather harder in practice than theory. From Posta Dente di Zenghiaro, beat the point of your opponents spear up and to your right. Ensure that it ends with the point directed at your opponents face. The forward momentum of the horse will cause your opponent to impale themselves.
As discussed in the explanation of the master play, having a horse thunder past you at such close range is a psychologically overwhelming experience. Even more so when it is being ridden by an opponent with a dangerous weapon and deadly intent. The hardest part of this play is keeping a clear head.
Timing is the key to making this work The greatly foreshortened view of your opponent coupled with the speed of the horse make it much harder than it sounds to guage the distance and timing of your beat. Also, of course, you only get one opportunity to make the attempt work.
Even if you avoid the spear point, you are still in danger of being run over by the horse. If you need to step offline, move your back foot to the left in the instant before the beat starts. Move your front foot also to the left after the beat, but before making contact with the point
You need to be far enough to the side to avoid the riders knee as they pass, but still close enough that you hit your opponent reasonably straight on.