Sylvester Stallone is not a real boxer. Although his portrayal of boxer Rocky Balboa seems to be pretty believable, Stallone has not trained professionally to become a boxer. Relying on his training for the Rocky franchise, Stallone once tried to fight Earnie Shavers in one of his movies. However, when Stallone asked Shavers to punch him harder to make the fight look realistic, Shavers knocked him with just a single hit. After this, Stallone fired Shavers and hired another actor in his place.