Regarding Ketchel-Johnson...

The two fighters made a deal. Johnson would not try to hurt Ketchel (who was only a middleweight), and would purposely let the fight drag out and go the distance. In exchange, Ketchel wouldn't try to throw many punches, and would let Johnson win a decision.

For some reason, Ketchel decided to throw an enormous right hand, and he knocked Johnson down. Johnson was stunned by the punch because the agreement was to not try to hurt one another, so he was never expecting the punch.

Johnson got pissed, got up, and knocked Ketchel out cold with one punch.