The seven-minute fight at the end of the movie took nearly four months to shoot. Jackie Chan indicated that one day's filming typically produces three seconds of usable film.
Jackie Chan actually crawled over the burning hot coals two times. He felt he "didn't have the right rhythm" the first time he did it.
Director Chia-Liang Liu and Jackie Chan clashed often during filming. Among their disagreements, Liu had a particular style of filming which involved quick tracking shots, slow-motion, and the use of wide-angle lenses to play with perspective, which Chan didn't appreciate, Liu wanted to have more of the realistic Huen-Gar style of fighting, whereas Chan felt the fans wanted more of the drunken style, and Liu wanted to use wires during the fight scenes, to which Chan was categorically opposed. Liu eventually left the movie, with Chan taking over as director for the final fight scene.
The fight at the end was originally to be Jackie Chan versus Ho-Sung Pak, but Ho-Sung Pak repeatedly strained his ankle. Instead, Chan had his personal bodyguard Ken Lo train intensively (lots of stretching and fast kicking) for three months to take the part.
The drunken boxing style exists in real life, originating from China. In Chinese, it is called "Zui Quan" (sometimes called Zuijuquan). But unlike in the movie, it is dangerous to perform the art while drunk, because serious injuries can occur.