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At the start of a TFC bout 2 teams of 5 take each other on in a brutal fight YouTube/team fighting championship

Concerns are being raised about a brutal new team fighting sport in which two teams of five engage in a brutal battle using fists and feet until only one is left standing.

Team fighting championship (TFC) started in Russia and has now spread to other countries including the US, Poland and Latvia. A typical bout lasts just a couple of minutes, but is so brutal that many competitors are left bleeding or unconscious.

Although there are rules involved in TFC, and five referees inside the ring to ensure they are followed, it is considered acceptable to keep clubbing a man in the face when he is on his back, kick him when he is down, and for two or more to team up on one unlucky opponent.

TFC is considered so brutal that even though cage fighting and "Ultimate Fighting" are allowed it is currently banned. However the US does have a TFC team which recently competed in an international tournament in Latvia.

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The competitors chase each other round the ring inflicting as much damage as possible YouTube/team fighting championship

"First, everybody did boxing, then kickboxing got popular, then MMA became the next thing," TFC USA head coach Jody Poff explained to Vice. "As a sport, we're going to go through the same growing pains as MMA [mixed martial arts] and the UFC went through. Yeah, we're a little crazy, but we're pro athletes and we want to explore what's next. The next level."

The rules of TFC are broadly the same as those of the Japanese-originating PRIDE fighting championship, which started in 1997.Each team must weigh a total of 550kg and there is no audience: the scrap takes place in a ring in an empty warehouse, which makes it sound oddly reminiscent of Fight Club - except without the Brad Pitt/Edward Norton bromance.

"It can get ugly fast once guys start dropping," said Poff. "But there are five referees in there with you, and they are watching everything. So in a way, by the time it gets mismatched, it's pretty safe. In a normal fight, there's only one ref."

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Even when a man is on his back it's considered legal for 2 or more opponents to lay into him as he lies helpless on the ground YouTube/team fighting championship

To those uninitiated in TFC, it seems like total carnage: just ten men chasing each other round a ring attempting to inflict as much damage as possible, though head-butts, spitting, kicks in the groin, biting, and blows to the Adam's apple are all banned. Even so, injuries can be horrific.

"The fights happen and they are over quickly," says USA fighter Sean Barnett. "It's not a street fight. There is strategy. But once one guy goes down, everything changes fast."