That isn't a lance duel. That's a joust. A duel is a fight to settle a disagreement. A joust was a mixture of practice for war and a type of sport.

Two riders riding towards each other at speeding and trying to hit the other with their lance is the basis of a type of joust however what happens next depends on the type.

A joust of war would use sharp lances and the idea was to knock the other person off their horse. In practice you would have to be pretty good or pretty lucky to manage this in one hit. Armour of the time was designed to make lances glance off the armour rather than absorbing the full force of the blow. In recognition of this points might be awarded based on where you hit your opponent.

A joust of peace would use blunt lances designed to splinter. In later periods there was also a barrier between the two contestants. In this case points would be scored by breaking your lance against the opponents armour. Again in later periods specialist jousting armours were developed that provided extra protection on the left side (the side most likely to be struck). Multiple charges might be made to establish a winner.