Swamp soccer.

Mucking around in a swamp has morphed into a sport. Last July, player Callum Garret sloshed through a boggy field during the United Kingdom Swamp Soccer tournament.

The key ingredient to this mud-splattering sport is water. Without it, the playing field would consist of billions of loosely arranged dry soil particles.

To transform the field into a sticky mud puddle, swamp-soccer organizers dump gallons of water onto the dirt. Because of water's surface tension, water molecules stick to the surfaces of soil particles, forming tiny water-bridges between the particles says Peter Schiffer, a physicist at Pennsylvania State University. This glues the soil together in a mucky mess, which gives players quite a workout.

With each step, Garret's feet sink into the muck, squeezing out the air from between his feet and the mud. That causes the air pressure above his foot to be much higher than beneath his foot. This difference in pressure creates suction, a force that holds his feet in the mud.

Extracting each foot from the mud's suction hold takes legwork. "It's all about strength and stamina," says Stewart Miller, the managing director of Swamp Soccer UK Ltd.

To stay on top of their game, and the mud, the players have devised some tricks. For one, they keep their leg muscles fatigue-free by passing the ball a lot. "The ball does the work rather than the players," says Miller.

Once the ball hits the field, the mud's suction often grabs hold of it. This muddy ball trap can cause a blunder. "Because people are used to the ball rolling along a dry soccer field, when the ball gets stuck in the mud, they run right past it," says Miller.

No trick can keep the players from slipping and sliding. At the game's end, most players are plastered with mud from head to toe. The uniforms would give any laundry detergent a stain-fighting workout.