Slap fighting: Is it the next big sport or just stupid?

The competitors stand rigidly upright with their hands behind their backs, waiting to absorb a brutal slap to the face.

When the open-handed blow is delivered, there's a sharp sound and the reaction can be dramatic. Some fighters barely move, while others stumble backward or fall to the floor. Some are knocked out.

It's a craze that started in Eastern Europe, with a few viral breakout stars finding fame on YouTube.

Now UFC President Dana White is selling slap fighting in America as the next big thing in combat sports, putting his money and the resources of one of the world's foremost mixed martial arts organisations behind the Power Slap League. 

"It’s a home run,” said White, who is among several UFC officials involved in the league.

Some slap-fighting beatdowns have gone viral, including a video from eastern Europe showing a man who continues to compete even as half of his face swells to seemingly twice its size. Such exposure has led to questions about the safety of slap fighting, particularly the risk of chronic traumatic encephalopathy, or CTE, a degenerative brain disease believed to be caused by repeated blows to the head.

In the US, the Nevada Athletic Commission has sanctioned the league for competitions in Las Vegas. A former chairman of the commission, which regulates combat sports in Nevada, says approving the league was a mistake.

Chris Nowinski, cofounder and CEO of the Concussion Legacy Foundation, agrees, calling slap fighting “one of the stupidest things you can do.”

“They’re trying to dress up a really stupid activity to try to make money,” Nowinski said.

White and the competitors remain unfazed, comparing commentary on slapping to the negative reaction the UFC faced in its infancy more than 20 years ago.

“I