The Thundering Mantis [1979, Martial arts, DVD5]

Ah Chi (Ka-Yan Leung) is obsessed with the martial arts and, more often than not, his kung-fu clowning gets him into trouble. One day he gets into a fight defending the locals from a violent thug who turns out to be an enforcer for tong boss Hsia (Eddie Ko) of the notorious Jade Brotherhood. In retaliation, Hsia forces Chi's martial arts master to expel him. Masterless and working for a fish vendor, Chi meets a crafty kid (Yat Lung Wong), whose uncle Chow Tung (Simon Yuen) is a master of the Insane Mantis style. Though the crotchety old man refuses to teach Chi his technique, Chi picks up what he can in secret. Master Chow soon relents after Chi is badly beaten in yet another battle with Hsia's goons. Insane Mantis instruction now begins in earnest with great acrobatic acuity. Eventually, however, Hsia and his lackeys ambush and kill both the fish vendor and the old master which, in turn, completes Ah Chi's descent into total insanity. Emulating praying mantis behavior, Ah Chi unleashes an outright cannibalistic rage directed against the Jade Brotherhood's big boss himself!