Muhummad Ali was involved in a controversial knockout in 1965.
Boxing lends itself to controversy on a regular basis.
Sometimes the controversies involves the way a fight finishes. Perhaps it appears that a fighter was knocked out, but he's allowed to continue because the referee got the count wrong.
Sometimes it's because a lesser fighter stops a more popular or favored fighter with a series of unsuspecting punches.
In other cases, there may be rumors that the fix was in.
Here's a look at some of the most controversial knockouts (and one non-knockout) in boxing history.
When Gene Tunney defeated hard-punching Jack Dempsey in 1926, calls for a rematch were swift and vociferous.
The two met one year later in Chicago. More than 100,000 fans crowded Chicago's Soldier Field, and in the early rounds, Tunney used his boxing skills to move ahead on points.
However, in the seventh round, Dempsey knocked Tunney down and started dancing around the ring in celebration instead of going to a neutral corner.
As a result, Dave Barry delayed starting the count on Tunney. He directed Dempsey to a neutral corner. By the time Barry started counting, Tunney had been down several seconds.
Tunney rose before the count of 10, but those at ringside estimated the champion was down for 12 to 15 seconds, meaning he was knocked out (via ChicagoTribune.com).
For years, Tunney said he could have gotten up but was trying to rest and regain his bearings. Others say Dempsey would have won the fight and should have regained his title.
Jack Johnson was one of the most controversial fighters in boxing history.
During his run as boxing's dominant fighter in the early part of the 20th century, he was reviled by white America because he refused to take on a subservient role and that was shocking at the time.
He was also a relentless powerhouse in the ring, and when he agreed to fight huge Jess Willard in 1915, few thought "the great white hope" would be able to compete with Johnson.
However, when the bout in Havana, Cuba, reached the 26th round, Willard let loose with a combination and knocked Johnson out.
Johnson later said he took a dive in the fight (via Coxscorner.com), but the fight films (above) show he was hit by a barrage of hard punches.
Cassius Clay stopped Sonny Liston to win the heavyweight title in 1964.
There were immediately calls for a rematch because Liston had been an overwhelming favorite before the fight because of his strength and punching power.
However, Clay's speed and sharp jab frustrated Liston and led to a TKO.
The rematch was fought in the unlikely location of Lewiston, Maine. Liston was badly out of shape for the fight. New York Times columnist Dave Anderson noted that he looked slow and ponderous in training, unable to even jump rope.
By the time of the rematch, Clay had changed his name to Muhammad Ali. He used his left jab and circled to his left and peppered Liston. Ali then shifted his weight, stepped to his right and hit Liston with a quick right that was not a power punch.
Liston never saw it and went down. By the time inexperienced referee Joe Walcott picked up the count, Liston was getting up and the fight continued.
However, Walcott was told by the timekeeper that Liston had been down for 10 seconds. At that point, Walcott stopped the fight, and Ali won by a controversial first-round knockout.
Jack Sharkey was one of the most talented heavyweights in 1930. He fought champion Max Schmeling for the title.
Sharkey was getting the best of Schmeling in the early rounds, and he delivered a hard shot to Schmeling's midsection that sent the German down to the canvas.
Schmeling was counted out. However, the punch was ruled a low blow, and Schmeling was called the winner on the foul blow.
Sharkey would later defeat Schmeling in 1932 to take the heavyweight championship.
Willie Pep, the former featherweight champion, was considered one of the most skilled and game fighters during his legendary career.
He was on an 18-fight winning streak when he fought lightly regarded Lulu Perez in 1954. Perez was not a hard puncher, but he sent Pep to the canvas three times in the second round and won via the three-knockdown rule.
The KO was controversial because Pep seemed to have Perez outclassed, yet he not only lost the fight, he got stopped early.
Pep would win his next three fights and continued to box through 1960. His career record of 230-11-1 is sensational, but the loss to Perez is a black mark on his record.
Roberto Duran was considered one of the greatest fighters in the second half of the 20th century.
He was a skilled boxer who could diagnose an opponent's weakness and exploit it, but his primary asset was his explosive punching power.
He not only knocked out many of his opponents, he also hurt them badly with his "hands of stone."
However, when he fought Sugar Ray Leonard in a 1980 rematch, Duran was frustrated by Leonard's quickness and left jab.
In the eighth round, Leonard wound up for a hard right hand, stopped in his tracks and sent a quick left jab into Duran's face. That maneuver humiliated Duran (via ESPN.com). He later told the referee "No Mas," and quit fighting in the middle of the round. The official ruling was an eighth-round TKO for Leonard.