The Octagon (1980)

Scott's life is plagued by two kinds of flashbacks. First are the childhood memories of the rigorous training he and a friend endured under a martial arts master. The second is of a mission Scott went on that ended with him watching his friend get murdered. Scott later becomes drawn closer to a vicious crime ring known as The Octagon. As he gets closer to the truth, Scott learns that these may be the men that murdered his friend so long ago.