The movie is about a boy and his mom move to a small town his mom got tranford for work. Well he gose for his first day of high school and well after his fisrt class he gose to the library and he sees this girl sitti at the table ad he starts talkig to her but the her boyfriend walks in with his frieds and the kid leaves and then after school thoughs guys jump I using mixed martial arts and karatay well then a couple days later they jump him agai in the gym well a janitor sees wuts going on and jumps in and he knows keratey well be feds them off and he help the kids heal the thie kid convinces the janitor to teach him martial arts well he dose then tords the end the keraty instructer who's been teaching the other kids sees the janitor and realizes that he's the one who killed hus brother in the beginning of the movie cause the janitor was a cop and got shot so he quite the force and became a janitor done at the high school can any tell me the name of the movie

Film is called showdown and is from 1993.
Search for it on Google or imdb, sounds like you are looking for the first one in the series.