Has this ever happened?

[levi#1BoxingFan]

Im not sure if this has ever happened or if its even legal (im not the all knowing of boxing), but why don't big time fights ever go 100/0 or winner takes it all? It may sound ridicoulous but think of the hype that it could create! It would make both fighters fight to the finish creating much more exciting bouts! I know it would never happen but what if Mayweather and Pacquiao did this? You have two of the most confident fighters who both say they will win, so why doesnt anyone put their money where their mouth is and play the game of winner takes it all! Like I said I dont even know if this is legal, but if it isn't, why not?

Would you work for nothing , would be my question ?

I'm mainly talking about the Vegas main eventers, the ones who already make millions a fight. (Mayweather, Pacquiao, cotto, B-hop....ect). To me thats the whole point, its high risk but high reward. Heck they're in vegas, why not act like it! Besides its not like their lives are ruined if they dont get paid for one fight, "I'm sorry jr., but your puppy can't have that rolex like I promised....Im sorry but daddy didn't get paid, but you can still have yours!"