This is one thing all noble hearthlings who want to earn honor in sport want, but how to do?
I say jousting should be similar to archery, in the way you aim. There will be a short delay before your lance becomes active, and the lance cannot change direction while "aimed" you are only able to move only in a single direction, the direction your lance is pointing.
The hit detection could be similar to an arrow? but unlike regular unarmed and armed combat.
It is essentially a third system of combat, reliant on horse mounted movement, and precise control.