Crossfire is a home computer video game created by Jay Sullivan and first published by Sierra On-Line in 1981. It was inspired by the arcade game Targ.
In Crossfire, the player uses the keyboard or a joystick to move left, right, up and down among an array of blocks, avoiding incoming fire and dispatching enemies. The playing area consists of 42 blocks (7 rows by 6 columns), through which there are six vertical alleys, five horizontal alleys, and 30 intersections. The player can move and fire in any of the four directions, but can only stop in intersections.
Along the left, right and top sides of the playing area are 16 pockets, each of which holds four enemies, one of each variety. These enemies emerge and move among the blocks, firing at and attempting to collide with the player. The enemies differ only in appearance, not in power or behavior. Like the player, the enemies can move and fire in any direction, but aren't as fast. Unlike the player, they never run out of ammunition.
Within four blocks near the middle of the playing area are four bonus items. Over the course of a level, each one briefly emerges before going back into its block. Capturing the bonus items grants 100, 200, 400 and 800 points.
The player can fire only a limited number of shots before having to reload. In early rounds this number is around 30, but drops as the levels progress. When ammunition runs low, a cluster of four pulsing white dots appears (usually at the most distant intersection) marking where the player needs to go to reload.
Play begins with three ships; an extra one is awarded every 5,000 points. The level ends when all the enemies are destroyed.
Source: Wikipedia, "Crossfire (video game)", available under the CC-BY-SA License.