Similar movie

I have not seen this movie - Neds, but the plot is bit similar to one movie I have been desperately looking for, for ages! I saw it about 20 or 25 years ago, when I was a child, but I still remember the movie a bit. I want to see it again! It was about some street gang of teenage kids. The leader got into some fight, and hit his head against a wall, which gave him a bad brain injury. He became mentally ill and is not who he used to be anymore. I remember I was so moved with the movie as a kid. Please help me find it, thank you! Must be a movie from 80s.