Nightmaster (1988)

Steve Beck (Vince Martin) is a Karate instructor, Robby Mason (Tom Jennings) his prize student. Beck is using drugs to give him an edge. Guy Duncan (Craig Pearce) is Beck's drug connection that threatens to expose Beck as a user then Beck kills Duncan, but Robby was witness to this. Robby confronts Beck about the killing, during the karate championship. Beck tries to kill Robby during the match and again afterward in the street.