Thursday night is fight class at Joe Diamond's Mixed Martial Arts academy at 43 N. Third St. About two dozen students spar on the center's blue training mats. Most students are paired off in teams of two: One student holds cushioned pads on each hand, the other circles, whipping off lightning-fast combinations of jabs, crosses and kicks.

Kevin Poznek, 22, lean, muscular and a first-level instructor in muay Thai — a style of kickboxing that allows elbows, knees and low kicks — seems to possess the most powerful foot of the night. He warms up on a heavy bag, taking a quick two-step before unloading a series of thunderous kicks.

"I used to practice my kick on spare tires," says the South Jersey native proudly. "And rub the ridges of glass Coke bottles up and down my shin, to harden the skin."

Other students grapple on the mats and practice their jiu-jitsu chokes, holds and locks on one another, twisting into grunting, contorted human pretzels of pain.

Next Friday night, Dec. 10, the students will have the opportunity to showcase their ass-kicking talents at Vengeance, Pennsylvania's first-ever sanctioned amateur Mixed Martial Arts tournament.

Mixed Martial Arts (MMA) is the umbrella term for various fight competitions that have emerged from the no-holds-barred, pay-per-view Ultimate Fighting events which began airing in 1993. In MMA, martial arts specialists of all stripes — karate, judo, muay thai, submission wrestling, jiu-jitsu, etc. — square off in matches that often turn brutal and bloody. Because of the violent nature, many states have shied away from sanctioning MMA events.

While Pennsylvania Athletic Commissioner Humberto Perez can sanction amateur events like Vengeance, he has been lobbying legislators in Harrisburg to consider sanctioning a professional MMA circuit in Pennsylvania. The proposed circuit would be less violent and more regulated than Ultimate Fighting.

"Mixed Martial Arts is a growing sport, a billion-dollar industry worldwide," says Perez. "Plus, there are roughly 65 MMA schools in Philadelphia … these fighters should have a place to compete."

Vengeance, which will be held at the Northern Liberties Recreation Center and feature only amateur fighters, will be an opportunity to showcase the more regulated version of the sport to unsure state officials, says Perez.

"The most important thing is the safety of the fighters," says Perez. "We've regulated out some of the hardcore stuff."

Unlike in Ultimate Fighting, there will be no ground fighting allowed, which means a fighter cannot mount his opponent and punch him into submission — a technique dubbed the "ground and pound." There will be no downward strikes and a fighter will not be allowed to pull an opponent's head into an incoming, punch, knee or elbow strike. All fighters will wear headgear, shin pads, and six-ounce gloves. Fights will consist of three two-minute rounds, as opposed to the five-minute rounds in Ultimate Fighting.

Around Joe Diamond's academy, there is some disappointment about the regulations.

"A lot of us would rather have it as an Ultimate Fighting event," says Jason Gleichman, 30, a professional chef at Old City's Eulogy and a student of Diamond's who will be making his MMA debut at Vengeance. "We all train equally hard on our ground techniques."

Still, even with the additional safeguards, Vengeance won't be for the faint of heart. Fighters are allowed to punch, kick, knee and elbow. And six-ounce gloves offer as much cushioning as a heavy-sock wrapped around a fist.

A second MMA tournament is tentatively scheduled for mid-February at the Armory on Roosevelt Boulevard. But everything depends on the success — and safety — of the Vengeance tournament, says Perez.

"If everything goes fine, then we'll be able to hold more shows," he says. "Maybe establish an amateur league and then, eventually, with the state's approval, a professional division."

"Professional MMA would change sport as we know it in Philadelphia," predicts Perez, admitting that any professional league is years away.

New Jersey is one of the few states to have sanctioned Ultimate Fighting. According to Larry Hazzard, commissioner of the New Jersey State Athletic Control Board, the sport has been safe and successful.

"Thus far, I have found it less brutal — in the long run and in terms of long-range injuries — than boxing," says Hazzard, a former boxer. "And it has a committed following. Certain shows have packed the (14,000-seat) Boardwalk Convention Center."

But if something goes wrong — like a bad injury — at Vengeance? "Then that could be the end of it, period," says Perez, bluntly.

Joe Diamond sits in a folding chair, watching as his students progress through fight class training drills.

At 38, Diamond is an intimidating man with dark eyes and the build of a brick house: 5 feet 11 inches tall, 220 pounds, bulging arms and no neck to speak of. One of the most respected Mixed Martial Arts instructors in the country, Diamond has won more than a half-dozen national and world titles in karate, jiu-jitsu and MMA fighting, trained U.S. soldiers in hand-to-hand combat techniques, and next week will be in Thailand competing in a Thai boxing match.

In 1999, Diamond won the World Kombat Championship Open, a no-holds-barred tournament held at the University of Delaware.

"Everything but biting and eye gouging was allowed," remembers Diamond, smiling.

In the championship match, Diamond faced Michael Blake, a professional muay Thai fighter from New Mexico with devastating punching power. The two men exchanged blows before Diamond took Blake to the mat. Diamond mounted Blake and began to punch him but soon lost his positioning and found himself at the receiving end of a steady stream of blows. Somehow, Diamond says, he was able to maneuver Blake into a knee bar, an extremely painful submission hold that puts overwhelming pressure on the leg muscles. Most fighters in Blake's situation quickly "tap out" and submit. But Blake kept punching.

"So I put a little more pressure and that's when I heard it pop," says Diamond. "I didn't want to break his leg but he didn't want to give up."

Diamond says he plans to fight in the February MMA event at the Armory — if it happens.

And although he personally could do without the more restrictive rules, he admits they are needed to get the sport going in Pennsylvania.

"I want to make sure the future of the sport is safe," he says, still watching his fighters train. "If the fighters are trained and taught in the correct techniques, the rules we have now really limit the chance of a devastating injury."