The arcade version's eight-directional dual-joystick control scheme (one to move, one to fire) was implemented when the game's creator, Eugene Jarvis, had his injured right hand in a cast. He was unable to play the arcade game Berzerk, because the cast prevented him from pressing the fire button. The two joysticks made it possible to move and fire at the same time without having to use buttons.
Contributed by KidDivinegon