Boxing is one of the most brutal professional sports in the world. Fighters are paid big money to literally knock each other senseless.

Boxing great Muhammad Ali has been diagnosed with Parkinson's disease—a brain disease—since his retirement. Those who regularly suffer from severe head trauma, such as boxers, are especially vulnerable to this illness.

In such a combative sport, is there really a need for extra foul play? Almost every fighter has thrown a low blow or head-butted his opponent in a fight before, but this list puts a spotlight on the notorious cheaters.

These boxers used dirty tactics as part of their arsenal, and some of their legacies are even defined by it.  

George "Elbows" McFadden

Though he fought before everyone reading this article was ever born, George “elbows” McFadden could not be left off this list. Heck, his moniker is “elbows”—of course he would have to make this list.

He used his elbows as extra fists in the ring. His signature move was to throw a wild punch at his opponent, miss, and follow through with his elbow. He himself credited this maneuver with winning him a couple fights.

“It won me a lot of fights,” McFadden confessed years after he had retired from the ring.

Evander Holyfield

Evander Holyfield was a champion boxer who didn’t shy away from using cheap shots.

He used his huge head time and time again to momentarily stun and sometimes open up wounds on his opponents. In possibly his most grievous cheap shot, during a fight with Michael Dokes he head-butted and landed a devastating low blow at the same time.

The worst part about Holyfield’s cheap shots was that he wasn’t very slick. He would lead in with his head with no regard for where the referee was standing. Fighting would often be stopped for a few seconds for the other boxer to regain his composure.

Bernard Hopkins

Bernard Hopkins is an ageless fighter who, at 46-years-old, became boxing’s oldest champion after defeating Jean Pascal a couple weeks ago.

With that being said, Hopkins is well known for his less than classy antics. From holding-and-hitting, extra punches after the bell, hitting in the back of the head, to even faking low blows—Hopkins has mastered it all.

When once interviewed about his dirty fighting ways, he arrogantly replied that fooling the referee is a skill and a sign of a highly trained fighter. He finds himself on this list for such cockiness in accepting that he is a dirty, I’m sorry, skilled fighter.

Sonny Liston

Sonny Liston was once regarded as one of the greatest fighters since Joe Louis.

During a 1964 fight where he was heavily favored against the trash-talking Muhammad Ali, Liston was being dominated in the early rounds. In desperation, Liston told his corner to rub an ointment used to seal cuts on his gloves.

Ali claimed he was fighting blind for about two rounds after that. Astonishingly though, Ali ended up winning the fight with a seventh-round TKO.

It was never proven that Liston cheated, but this same event happened in two other fights during this era. Oh, and Sonny Liston participated in those other two fights as well. You be the judge.

Mike Tyson

Let’s see. Uppercut? Check! Left hook? Check! Bite my opponent’s ear off? Check!

In one of the most bizarre scenes ever in the boxing ring, Mike Tyson bit off a chunk of Evander Holyfield’s ear in a 1997 pay-per-view bout. The even more shocking part was as Holyfield was flailing around the ring in disarray, Tyson came over and shoved him, still wanting to fight.

Anyone who turns into a cannibal mid-fight, with millions of people watching, has no competition when it comes to playing foul. This moment will forever be one of the most gruesome acts ever in all of professional sports.