A movie were a teen gets in trouble a lot and a china man trains him in marital arts and gives him a ring with a dragon and a tiger on it. The guy at the end of the movie is in a warehouse fighting bad guys. Something I remember in the movie is the guy goes back to school to see his kid brother and kicks a football player in the halmet and breaks it.

The Perfect Weapon (1991) (http://www.imdb.com/title/tt0102655/)
You can watch it on YouTube (http://www.youtube.com/watch?v=UezijbnaKR8).