Over the long history of professional boxing, there have been only a few boxers who have completed their careers without a single defeat. Floyd Mayweather Jr. He made his debut in the professional ring in October 1996 at the age of 19; in his career as a professional boxer, Mayweather had 50 fights and won each of them in 27 of them he was able to knock out an opponent. In this video, we look at 5 cases when Floyd Mayweather Jr. was almost on the verge of losing.