Penn is the top-ranked welterweight mixed martial arts fighter in MMAFighting.net's world rankings. Mixed martial arts is a combat sport in which competitors may punch, kick, choke, throw and use other techniques.

Police said Pauoa, who was hit in the face, and another officer working at the club had gone outside to break up a fight among a large group of men. Police said the officers used pepper spray to disperse the crowd.

Penn, who police said was in the crowd, allegedly hit Pauoa with a blind-side punch to his left eye and tried to run away, police said. Pauoa ran after Penn and tackled him, but was immediately jumped by several other men in the crowd who tried to pull the officer off Penn, police said.

At that moment, District 6 patrol officers arrived, pulled the men off Pauoa and arrested Penn on suspicion of assaulting a law-enforcement officer in the first degree, a Class C felony.

If convicted, Penn faces up to five years in jail. His bail was set at $20,000.

Pauoa was taken by ambulance to Straub Hospital, where he was treated and released.

Jim Boersema, co-owner of Zanzabar, said he hired two uniformed special-duty police officers for Saturday's post-fight party and sectioned off a portion of the club to give the fighters privacy. He said there were about 600 people in the club at closing time.

"We didn't have any problems," he said.

Penn's brother, J.D. Penn — president of Rumble on the World Entertainment, which promoted Saturday's fight — said the company is looking into the arrest. Rumble on the World is the largest promoter and organizer of mixed martial arts competitions in the state.

"It's definitely not good; we're still investigating everything that happened," J.D. Penn said.

He said further inquires about his brother's case would be handled by Honolulu attorney Michael Green. Green acknowledged yesterday that he is representing Penn but declined further comment.

Penn did not fight Saturday night but attended the fight to support his brother and fighters who compete and train with B.J. Penn's Mixed Martial Arts Academy in Hilo. Rumble on the World is a Hilo-based company that produces and markets mixed martial arts events and TV productions.

Penn also runs the BJ Penn Jiu-jitsu Academy in Kona.

The arrest was the second recent negative allegation against Rumble on the World Entertainment. Last week, police opened an investigation into allegations that a Waimanalo boxing coach entered a 14-year-old boy into a "Rumble on the Rock" qualifying event against a 32-year-old professional fighter March 11. The arrest and investigation come at a time when the Legislature has passed a bill with new regulations for the sport.

Gov. Linda Lingle has until July 12 to sign Senate Bill 768, which addresses conduct and permits for martial arts fights and requires promoters to put specific safeguards in place. It also would levy a fine of up to $10,000 for infractions.

The state believes the rules are necessary to regulate a violent activity that's gaining in popularity. The "Rumble on the Rock 6" in November 2004 sold more than 8,000 tickets, according to the company.

J.D. Penn acknowledged that his brother's arrest, coupled with the allegations of a minor fighting a man, are damaging.

"It's definitely not good at the same time, but when it rains, it pours," he said yesterday. "That 14-year-old (fighting in a match), we would never let that happen. We're investigating to figure out what went wrong."

He said he supports regulation as a way to legitimize and recognize the sport. Regulation also allows the sport to move into the mainstream, he said, and would force everyone involved to play by the same rules and work together, he said.

In less than two years, Rumble World Entertainment, formerly Prodigy Productions, has transformed "Rumble on the Rock" from a small Hilo-based show into a globally recognized event broadcast in 90 countries, according to a company press release.