Whats the reason that mike chambers is in the hospital in the book That Was Then, This Is Now?

Mike is in the hospital because he was beaten.
Mike is a young man who saved a black girl from being beaten by a group of white boys. Prejudices run high in the neighborhood where they live, and if Mike hadn't been there, she could have been gravely injured. He drove her home after saving her to make sure that she wasn't harassed again.
Unfortunately, Mike was beaten for his kind act. A group of African-American boys saw the girl and Mike together. She said that Mike beat her, and the boys beat him as punishment for what they believed he'd done to her.
Mike says he can almost understand why the girl lied. It didn't make him hate African-American people. However, when Mark hears his story, he says that he wouldn't have the same understanding. He says that anyone who betrayed him would be someone he hated. This foreshadows the end of the story, when Byron turns Mark into the police.