When his unknown opponent suffers a brain haemorrhage in the ring at a local tournament, a rookie fighter must discover the boxer’s identity and find his family to gift his prize money to them.

There seems to be a disconnect between the character development and the outer goal. In most good stories the MC needs to overcome a character flaw, this process will make up the inner journey as a pre request for achieving the outer journey goal. In other words, your protagonist needs to change as a person before he can give them the prise money.

What character flaw does he have? How will he change?

This may seem like a small issue, but in this kind of story, you need a good inner journey. Otherwise, you've got a good guy doing a good thing with little to no obstacles - no conflict and no drama.

Why does the rookie have to give the prize money to the family? What is at stake if he doesn't do it?

I like the premise, I think this could make a good road movie.

Your lead needs a partner, someone to go on the road with him.?