Pete Rademacher fought for the heavyweight title in his pro debut

Not really his fault but Tim Tomashek literally came out of the crowd to fight Morrison for his WBO strap after Mike Williams refused to come out of the dressing room. There was a similar situation to this when Isidro Garcia was picked out of the crowd to fight Jose Lopez for the WBO flyweight title....difference was he won

Isidro Garcia vs. Jose Lopez - Boxrec Boxing Encyclopaedia