Slap fighting: The next big thing, or unsporting stupidity?

Ryan Phillips slaps Rob Perez at a Power Slap event in Las Vegas. (Courtesy/AP)

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 report and the reaction can be dramatic. Some fighters barely move, while others stumble backward or fall to the floor. Some are knocked out.