Ashita no Joe

Ashita no Joe (or Tomorrow's Joe) is a classic anime about a delinquent who learns to box. It inspired Hajime no Ippo.

Plot
Joe Yabuki is a young man living in the slums of Tokyo. But, one day he meets Danpei Tange, a former boxer, who discovers his potential in boxing and tries to make him into a champion. Due to petty crimes, Joe is sent to a juvenile prison. There Joe mets Toru Rikiishi, a promising boxer, who knocked him out with one blow when he attempted to escape prison. Slowly but surely, Joe realizes his own potential. Joe begins his boxing life, step by step, with only one goal in mind... To Defeat Toru Rikiishi !!