Castle Guard is based on the old Atari 2600 (and arcade) game called Warlords. The basic premise is that you have to knock down the opponents castle, by batting a large fireball around with your paddle (which can move both horizontally and vertically). You can play against a computer opponent, or another person (there is a 3rd mode, which is computer vs. computer, which is basically a demo mode). Unlike the original version (or other Coco versions such as Tom Mix's War Kings), you do not have to break down a barrier, but you gradually cause the castle to sink completely into the ground.
Title: Castle Guard
Author: ??? (The Image Producers)
Publisher: Radio Shack/Tandy
Released: February 1983, written in 1982
Requires: Color Computer 1,2,3, 16K RAM, joystick, cartridge.