Description taken from Arcade version of this game

Joust has you controlling a lance-equipped knight in a quest to knock rival knights off their mounts. The twist? Instead of galloping along the ground on a horse, your knight rides an ostrich with the ability to fly. Basic movement is initiated with the joystick, while flapping the ostrich's wings involves repeatedly tapping a button. To win each joust, your lance must be positioned above those of your opponents. Should two lances meet at the same height, both riders will bounce back unharmed.

After losing a joust, the opponent will turn into an egg, which will either disappear into the lava at the bottom of the screen or land on one of the suspended platforms on the playing field. If the egg falls on land, you must quickly grab it before it hatches into a new, more powerful rider. Three types of opponents are as follows: Bounders, red riders worth 500 points apiece; Hunters, gray riders worth 750 points apiece; and Shadow Lords, blue riders worth 1,500 points apiece.

While you begin the game with five lives, extra riders are earned for every 20,000 points scored. Play continues until all riders on the screen are defeated, at which point a new wave of enemies will appear. Future waves feature pterodactyls flying across the screen, disappearing platforms, and the appearance of a lava troll, who will gleefully grab any rider flying too close to the lava's surface. Two players can also compete simultaneously on the same screen, with the second knight appearing on a stork instead of an ostrich. ~ Scott Alan Marriott, All Game Guide