LONDON (Reuters) - Steven Hopwood has traded the cut and thrust of financial markets for the jabs and kicks of cage fighting -- a fast growing mix of martial arts and an old-fashioned pub brawl.

City trader turned cagefighter Steven Hopwood (R) punches during a fight in this September 29, 2008 file photograph. REUTERS/Vincent Garnier/www.rawsport.tv/Files/Handout

Fighting under the nickname “Hoppy,” the 36-year-old former equity trader entered an octagonal arena enclosed by a cage, where he faced a much taller opponent in his first contest as a professional cage fighter.

Wearing only shorts and authorized gloves, they went at each other with fists, elbows, knees and feet, using judo, karate, boxing and any other martial arts moves.

There’s no head-butting, eye gauging or biting. Elbow strikes to a downed opponent and groin kicking are also banned. Pretty much anything else goes.

“What I like about cage fighting is that you’ve got the ability to control what goes on,” said Hopwood, who worked at investment banks Panmure Gordon & Co and Henderson. “In the financial markets, you’ve got very little control over what you do. It’s not a science -- something you cannot control.”

From humble beginnings in Brazil in the early 1900s, there are now over 140 mixed martial arts events in Britain each year, and the sport is rapidly gaining in popularity in the United States and Japan.

Known in Britain as "Cage Rage" (www.cagerage.tv/), it is gaining in popularity fast, with cable television stations snapping up the rights to top bouts and competitions.

Rules differ around the world but in Britain there are usually three five-minute rounds, with a referee inside the cage to enforce what few rules there are.

Hopwood’s introduction to the sport came almost by accident.

Tiring of a life of long lunches and after-work drinks, he hooked up with personal trainer and leading British mixed martial arts fighter Neil “Goliath” Grove, hoping to get back into shape and relieve the stresses of his job.

“I’d had a baby, got a job, was getting older and fatter, and it was always tomorrow I’ll get myself fit,” Hopwood said. “Grove said to me, you’ve got all this raw power and you’re not doing anything with it.”

FIGHT NIGHT

After months of grueling gym sessions, Grove surprised Hopwood by arranging for him to fight in a Cage Rage UK contenders show, giving him only weeks to prepare.

Although an injury postponed his planned debut, Hopwood eventually faced his first opponent in a professional bout in September, in front of 3,000 spectators -- 300 of them friends, family and former colleagues -- and won.

“My greatest moment of my life was when my daughter was born but my cage fight debut came a close second,” he said.

Part of the appeal of cage fighting is the camaraderie, said Hopwood, a former private in the parachute regiment in the British army.

“I found myself in this new brotherhood, like being back in the army again. It’s a strange thing, going in there and getting physically beaten up -- and thanking the guy afterwards.”

Hopwood said he had a good conversation with his opponent, a school teacher, two days before the fight and they shared a drink afterwards.

His new sport comes at a cost -- in training he suffered a broken hand and metatarsal, fractured three ribs, pulled a hamstring, dislocated an elbow and two fingers, tore calf muscles and suffered a hernia.

Hopwood said he missed the banter of his former colleagues, but not the job itself or London’s financial district, which has gone through a crash since he left in July. “I don’t miss the City too much.”

“I was up there today and it was grim and sobering. It’s a very close knit industry -- certainly the equities side -- and I feel sorry for these guys.”

“There are good guys working and they are having to worry about having to pay the mortgage or having a job next year.”

Hopwood knows that he will have to return to his life as a trader one day, to support his young family, including his partner Sophie, one-year old daughter Grace, and another child on the way.

But he plans to continue with the cage fights, and has even promised to marry his partner if he wins his next two bouts.