The Substitute

The Substitute is a movie starring Tom Berenger, Raymond Cruz, and William Forsythe. Mercenary Shale's team is retired after a (not so) covert mission in Cuba. He becomes substitute teacher at his teacher fiancee's Miami high school...
When an inner-city Miami schoolteacher gets her knee broken after standing up to the school's gang leader, her mercenary combat specialist boyfriend goes undercover as a substitute teacher to take down the punk. Soon he discovers a conspiracy of criminals at work, and must reassemble his team from his last jungle raid to stop them.