Sammo Hung hired a personal trainer to help slim him down so he could more easily perform some of the acrobatic kicking combinations which he had devised for the project with his stunt team.
This is Yuen Wah's breakout 'villain' role. A long time Sammo Hung stuntman (who famously doubled Bruce Lee in the opening scenes of Enter the Dragon), Yuen Wah became the number one villain on screen in Hong Kong after his memorable performance as the general.
Most of the sequences in this movie were filmed for real, with the actors actually making full physical contact during the fight scenes.
Sammo Hung's original cut of the film was much longer, but it was heavily cut down before release. This is why original four minutes long Hong Kong trailer for the film shows bunch of deleted and alternate scenes, including many scenes from original first act of the film with all the main heroes in prison, being beaten up by guards, getting into fights with them and other prisoners, basketball scene which included another massive fight, and prison riot scene. The training scenes during which more background about all the characters was revealed were also cut out. No extended version of the film or any deleted footage was ever released.
Sammo Hung met his wife to be Joyce Godenzi while making this movie.