I’m pretty sure it was a webtoon or manwha
It’s about a delinquent (or strong guy in general) who gets into an accident and ends up in the body of a student at his school who killed himself (I think?) because he was heavily bullied at school and I think at home (?). He starts to fight back and the students call him mad dog. He’s small with black hair.
This attracts the attention of someone who knew him in his other life, a white haired asshole (maybe he is the mad dog??) who starts thinking that the delinquent was reincarnated into the body.
I can’t remember any more than that, thank you in advance.