A victorious Jack Johnson stands over James J Jeffries as he fails to get up from the canvas in the 15th round. Photo by PA Images via Getty Images.
Muhammad Ali steps away from a punch thrown by Joe Frazier during their heavyweight title fight at Madison Square Garden in 1971. Frazier became the undisputed heavyweight champ of the world by winning a unanimous 15-round decision. Photo by Bettmann / Getty Images.
Billy Conn hits the canvas after being hit by punch thrown by Joe Louis during bout at the Polo Grounds. Louis retained his World Heavyweight Title, knocking out Conn in the 13th round. Photo by NY Daily News Archive via Getty Images.
Sugar Ray Leonard raises his fists in celebration after defeating Thomas Hearns at Ceasars Palace in Las Vegas, Nevada on September 16, 1981. Sugar Ray Leonard defeated Thomas Hearns in the 14th round with a declared knockout. Photo by Focus on Sport/ Getty Images.
Joe Louis stands over his fallen foe, Max Schmeling, after battering him to the canvas. Photo by NY Daily News Archive via Getty Images.
American heavyweight boxing champion Joe Frazier kept his title at the end of the fight called the "match of the century" against his compatriot Muhammad Ali at the Madison Square Garden, in New York, March 08 1971. Photo credit should read -/AFP/Getty Images.
Ken Norton is hit with a left jab from Muhammad Ali during the fight at the Sports Arena on March 31,1973 in San Diego, California. Ken Norton won the NABF heavyweight title. Photo by: The Ring Magazine/Getty Images.
Marvin Hagler poses with Thomas Hearns during a press conference to promote their upcoming fight on April 15,1985 in Las Vegas, Nevada. Photo by: The Ring Magazine/Getty Images.
Meldrick Taylor is hit with a punch from Julio Cesar Chavez during the fight at the Hilton Hotel in Las Vegas, Nevada. Julio Cesar Chavez won the WBC light welterweight title, IBF light welterweight title. Photo by: The Ring Magazine/Getty Images.
Marco Antonio Barrera celebrates after defeating Erik Morales in a fight for the WBC World Super Featherweight Championship at the MGM Grand Garden Arena on November 27, 2004 in Las Vegas, Nevada. Barrera defeated Morales in a majority decision after 12 rounds. Photo by Al Bello/Getty Images.
Aaron Pryor throws a punch against Alexis Arguello during the fight at the Orange Bowl in Miami, Florida. Aaron Pryor won the WBA World light welterweight title by a TKO 14. Photo by: The Ring Magazine/Getty Images.
View of people crowding around the ring at the end of the boxing match between American heavyweights boxer Muhammad Ali and Joe Frazier at Madison Square Garden, New York, New York, January 28, 1974. In a close match, Ali won on points and went on to meet George Foreman for the world heavyweight title. Photo by: Lane Montgomery/Getty Images.
Rocky Marciano drove his right mercilessly to the jaw of champion Joe Walcott to knock him from his throne in the 13th round of last night's title fight at Philadelphia's Municipal Stadium. A cloudy spray of water and perspiration makes a partial halo around the head of the champion who was "ex" eleven seconds later. Photo by: Herb Scharfman.
WBC heavyweight champion Larry Holmes survived blows like this in the 15th round from Ken Norton to score a split decision at Caesars Palace Sports Pavillion in Las Vegas 6/9. It was Norton's first defense of his title after it had been awarded to his in March. Photo by: Bettmann / Getty Images.
Defending middleweight champion Carmen Basilio exchanges blows with Sugar Ray Robinson during the sixth round of their title bout. Robinson won on a split decision to become the only fighter in history to win the middleweight title five times. Photo by: Bettmann / Getty Images.
Challenger Tony Demarco slumps to the canvas after taking a series of crashing lefts and rights from welterweight king Carmen Basilio in the 12th stanza of their title bout at Boston Garden last night. Moments later Referee Mel Manning stopped the fight as Demarco showed no signs of being able to defend himself any longer. Basilio was awarded the fight by a TKO at 1:54 of the stanza. Bettmann / Getty Images.
Clinging to the Ropes, Rocky Graziano puts up his right arm to ward off a right by Tony Zale, moving in for the kill in the third round of their middleweight title bout. Zale regained the crown he had lost to Graziano by a knockout in this round. Photo by: Bettmann / Getty Images.
Muhammad Ali smashes a right to the head of George Foreman. Photo by: Bettmann / Getty Images.
Tony DeMarco lies unconscious after he was floored in the 12th round on a TKO by Carmen Basilio during their championship bout at the Boston Garden on November 30th, 1955. Photo by Bettmann / Getty Images.
Gene Tunney's first fight against Jack Dempsey in Philadelphia; Dempsey on the ground in the 8th round. Photo by: ullstein bild via Getty Images.