Defender is the pack-in cartridge with the Adventure Vision tabletop system. Your objective in the game is to score as many points as possible by protecting the Earth and its human inhabitants from wave after wave of evil alien invaders. To achieve your objective, you are given command of the Defender, a powerful ship equipped with a laser cannon, hyperspace and smart bombs. The playfield in this game scrolls horizontally and you can fly and shoot in either direction.

As you cruise around the Earth, shooting aliens out of the sky, you will see humans walking along the mountainous surface of the planet. Frequently an enemy Lander will swoop down and abduct a human and attempt to carry him or her up to the top of the screen. If the Lander is successful, it and the human will turn into Mutants, which are quicker and trickier than Landers. To prevent abduction, you can shoot the Landers before they reach the humans, or you can shoot a Lander while it is in the process of abducting a human. The latter of these two strategies will release the innocent bystander, giving you a chance to score extra points by snatching the human out of the sky and carrying him or her back to the surface.

If you manage to eliminate all of the Landers and Mutants, you will move on to the next attack wave. From this point forward, you must also do battle with Pods, Swarmers and Bombers. Pods are free floating aliens that when shot release Swarmers, who are intelligent beings determined to destroy your ship. Bombers specialize in laying deadly space mines. A radar scanner at the top of the screen helps you keep track of offscreen enemies.

If at any point you allow all your humans to be abducted and/or destroyed, you will find yourself in the depths of outer space, facing fleet after fleet of Mutants. A game of Defender ends only when all of your ships have been destroyed. You gain an additional smart bomb and ship for every 10,000 points you score. ~ Brett Alan Weiss, All Game Guide