In 1963, when Muhammad Ali was still known as Cassius Clay, he went to London to fight Henry Cooper.
As he tended to do, Ali mocked his opponent before the fight, saying that Cooper was ”a tramp, a bum, and a cripple not worth training for” and he clearly saw Cooper as a warm-up for Sonny Liston.
That didn't last long. As you’ll see here, Cooper, despite being shorter and lighter, came at Ali relentlessly and in the 4th, amazingly knocked Ali down and very nearly out of the ring.
It really is one of the more amazing punches in boxing history. We expect people recognized that Ali had enormous potential although a lot of people also thought he would get killed by Liston. Cooper nearly derailed Ali’s ascension and Ali knew it because after the fight he said this: “Cooper’s not a bum any more. I underestimated him. He’s the toughest fighter I ever met and the first to really drop me. He’s a real fighter.”