When he was young, he used to prizefight regularly to earn money.

prizefight 是由 prize（奖金）和 fight（打斗）组成的复合词，字面意思是"为奖金而战"，特指"职业拳击比赛"。这种比赛通常以赢取奖金为目的，区别于业余拳击比赛。