Hauptman and others,The translation of the equestrian material from Fiore is all but complete.
The lance play is very simple: if you have a longer lance, you will make first contact. Therefore the person with the shorter lance should adopt a position (boar's tooth or woman's guard) to set aside the longer lance, driving home your point in the same movement. If the person with the longer lance sees the opponent with the shorter lance adopt one of these parrying positions, he is to aim at the head of the opponent's horse and make contact with the horse before the parry can be used. If both have shorter lances, a cat-and-mouse game of setting aside the opponent's lance and simultaneously driving home the point begins.
With swords, it is advised to adopt one of the parrying guards (preferably the boar's tooth), set aside his sword and then enter one of several variations on thrusting, cutting to the head, hooking with the cross or pommel to disarm, pommel strike to the face, clotheslining him off his horse, etc. What follows are wrestling maneuvers from horseback which closely resemble those on foot and rely on similar posta, along with the counters to them. There are techniques for taking the reins of the opponent's horse to turn it's head.
Recreating and practicing these techniques safely would be challenging. Most of them are made for use against an armored opponent, so the armor doesn't help you avoid injury that much.
It is very dangerous stuff, especially with the unpredictability of even a tested animal thrown in the mix. Some of it can be practiced at a walk, but that's all I would advise. They are clearly made for a serious application - not sport. People would land on their heads, under their horses, etc.
Take care with these. I think the application should be slow, careful and for demonstration purposes with trusted friends at half speed.
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Bob Charron