It's practically common knowledge that the medieval European knight wielded a lance. I'm also under the impression that they would (as need arose) fight with a sword (mace, axe, hammer, etc) from horseback as well. When it became necessary to change from one to the other in the midst of battle, how would this be accomplished? What happened to the lance when the sword was drawn? How did he get a lance when needed?
Mounted knights (and other gentlemen at arms) would ride into battle carrying their lance, with their sword in a scabbard hung from a belt on their hip. Other weapons like hammers and maces would be hung from the saddle by leather thongs. Spare lances wouldn't be carried into battle by the knight himself, at least not in the high and late middle ages when the lance gets longer and stouter.
Mounted knights (and other gentlemen at arms) would charge using a lance. Lances were generally 'one shot' weapons that would either shatter on impact or lodge in the body and need to be dropped. After the knight's lance was shattered or dropped, he would draw his sword or pick up a mace or warhammer to carry on hand to hand combat.