movie about a black boxer

I saw this movie more then 10 years ago. i'm guessing it is 90s movie. It was about young boy - he went to live (dunno what happened with his parents) with his grandpa or some other relative they lived in a house with a lot of people. That relative was a boxing trainer and the boy was training with him. I remember one scene when the boy went with (dunno who) to his first amateur match and he won in the first round. Then the (dunno who) guy phone called the relative (that trained him) and the conversation was something like:
"He won in 7"
"there aren't 7 rounds in amateur boxing"
"In 7 seconds"

I know it is very poor information but if someone can help i will be very greatfull.

It's Mike Tyson.