When world heavyweight champion Rocky “The Brockton Blockbuster” Marciano fought his last fight on September 21, 1955, at Yankee Stadium in the Bronx, New York, his final record was 49-0 with 43 stoppages.
Marciano came off the canvas in that final fight, being dropped in the second round for a two-count by ‘knockout king’ light heavyweight champion Archie ‘Old Mongoose’ Moore, 149-19-8 with 108 stoppages. He came back, dropping Moore twice in rounds six, once in the eighth, and was counted out in the ninth round at 1:19 by referee Harry Kessler.
Since then, there have been three boxers before Floyd “Money” Mayweather, Jr. retired with a 50-0 record on August 26, 2017, when he stopped MMA fighter Conor McGregor, making his debut in the tenth round at 1:05 by referee Robert Byrd.
Mayweather was urged by former heavyweight champion “Big” George Foreman to go for the record. He was smart enough to only average landing about three punches a round for nine rounds, carrying the novice McGregor before unloading on him in the tenth and final round.
Before this, on February 5, 2009, WBO, WBA, WBC, and IBF world super middleweight champion Joe Calzaghe reached 46-0 with 32 stoppages, retiring with “bad hands,” it was noted.
Another was Denmark’s “Super” Brian Nielsen, IBO world heavyweight champion, who reached 48-0 when former world WBC and WBA champion “Terrible” Tim Witherspoon, 55-12-1, admitted to this writer he took a “dive” for backers of Nielsen, being stopped in four rounds. Nielsen, in his next fight, was stopped by Dicky Ryan, 47-4, in the tenth and final round, whom he had on the canvas in the fourth round. Eighteen months later, Nielsen reversed it, losing in December 2000 by decision.
The other boxer was Larry “The Easton Assassin” Holmes, who was 48-0 when he was the light heavyweight champion, and 1976 Olympic Gold Medalist Michael Spinks, 27-0, defeated him on September 21, 1985. Seven months later, Holmes lost to Spinks again on a disputed decision.
Current WBC, WBO, and IBF super middleweight champion Terence “Bud” Crawford, with a 42-0 record with 31 stoppages, may be looking for one more fight before retiring.