what champion had the worst amateur record yet still obtained a world title as a professional, and how did he get that much improvement?
Might not be a champion, but Librado Andrade lost all but one of his amateur fights I believe. Was twenty something and one.
Marciano did fight as an amateur. In fact, he lost as an amateur after turning pro. Back then, you could have one fight fight as a professional and return to the amateurs if you felt the need to further hone your skills. I think I read Rocky's amateur record was around 8-4, but I'm not certain.
freddie pendelton won one fight out of 6 amature matches and then went on to beat roger mayweather, jorge paez, tyrone trice, tony lopez, livingston bramble and tracy spann for the ibf lightweight title.
i heard qawi's was nil....i dunno if that gets around the thread title becuase a pro kickboxer would technically have no wins as an amtuer boxer