Klitschko's feet came off the canvas when he was trying to put as much weight as he possibly could onto Povetkin's back. Its an illegal strategy he used to wear his opponents out and to prevent them from being able to box.If thats not a dirty tactic i don't know what is. Vitali was a much cleaner boxer. He rarely ever fouled or fought dirty.
Gatti did a ton of low blowing. I lost count of how many low blows he hit Rodriguez with. Wayne Kelly was pretty generous to Gatti by only deducting one point for low blows. He hit Robinson with a lot of low blows, particularly in round 9 of their rematch. The left hook knockouts of Rodriguez and Ruelas came immediately following left hooks that had strayed low.
I think Hagler was another fighter that always fought clean.He didn't need to use illegal tactics to gain an advantage.