INDIANAPOLIS, AUG. 14 -- On a day when the United States won six swimming gold medals in six races, the tension between anti-Castro demonstrators and Cuban athletes and officials escalated to violence for the second time.

American swimming victories in the women's 200-meter medley, the men's 200 butterfly, the men's 50 freestyle, the women's 800 freestyle, the men's 100 backstroke and the women's 4 x 100 medley, sent a sellout crowd into a star-spangled tizzy and gave the United States 21 gold medals in 26 swimming events, with one day remaining in the competition.

At the Indiana Convention Center tonight, nearly a dozen Cuban boxers, angered when anti-Castro demonstrators began tearing up a Cuban flag, rushed into the stands and punched at least two persons during boxing competition.

An anti-Castro demonstrator was arrested and two people hospitalized after the fights. Ramos Delemos, of Dayton, Ohio, was arrested and charged with disorderly conduct, said Indianapolis police spokeswoman Barbara Sinclair. Two people, both members of the Cuba Independent and Democratic group, were taken to a hospital with cuts and bruises.

A third member of the CID, an anti-Castro organization comprised primarily of former Cubans who moved to the United States, was treated for minor injuries at the center.

Cuban light heavyweight Pablo Romero, a two-time world champion, was seen punching demonstrators while his teammates tried to help out.

The scuffle was the second major incident involving Cuban athletes and anti-Castro demonstrators at the Games. A fight between an anti-Castro group and members of the Cuban delegation broke out at the conclusion of a Cuban baseball game Sunday. Before the game, leaflets urging Cubans to defect were thrown onto the baseball field.

Friday night's brawl began about 50 yards from the ring between the second and third rounds of a fight between Marc Menard of Canada and Jorge Migliasso of Argentina.

"It was definitely a provoked incident," said Jim Fox, executive director of the U.S. Boxing Federation.

Fox said about five persons were taunting the Cubans and began destroying the flag when Romero, followed by other members of the team, rushed into the bleachers.

In baseball, both Cuba and the United States won today, setting up Saturday's 12:30 p.m. game between the two unbeaten teams. Cuban pitcher Omar Ajete threw a perfect game for 6 2/3 innings today, before settling for a one-hitter.

"If we beat them, it'll be the second miracle in the history of amateur athletics," U.S. Coach Ron Fraser said. "It'll be just like the U.S. hockey team beating Russia {in the 1980 Winter Olympics}."

Cuba warmed up for the well-anticipated match by beating Venezuela, 15-1, in a game that went seven innings because of the 10-run rule. The United States beat the Netherlands Antilles, 14-1.

Today, Ajete came within a strike of his perfect game. There were two out in the seventh and final inning and he had two strikes on Jose Garcia Soto.

Ajete threw what appeared to be a perfectly placed strike three, which would have given him the perfect game. But American umpire Bob Wolfe called ball three. Ajete then threw ball four, a pitch that was not as close. The perfect game was gone, as fans sitting behind home plate -- including some disgusted major league scouts -- screamed in disbelief.

The next Venezuelan batter, Jesus Borjas, grounded into what should have been a game-ending forceout. But Cuban second baseman Omar Linares dropped the throw, leaving runners on first and second and forcing Ajete to pitch to another batter.

Miguel Casteneda hit what on many other days would have been a routine popup to the first baseman. But the wind kept sweeping the ball down the right field line, and it dropped in for a hit. No no-hitter.

The U.S. swimmers were led by Sara Linke from Walnut Creek, Calif., who swam the anchor leg of the women's medley relay and earned her fifth gold medal of these Games.

The United States dominated today to the point of finishing one-two in every individual event. Tom Williams, a University of Iowa graduate, recorded a Pan American Games record of 22.55 in the 50-meter freestyle, edging Arkansas' Mike Neuhofel.

Bill Stapleton of the University of Texas won the gold in the 200-meter butterfly with a time of 2:00.70, edging the University of Florida's Jamye Taylor, who recorded a personal-best time but lost at the touch.

Susan Habermas from Gaithersburg, Md., and Texas A&M swam the 200-meter medley in 2:18.22 to beat teammate Cathy Ritch, a New York high school student. Tammy Bruce, another Florida Gator, won the 800-meter freestyle. The silver medalist was Debbie Babashoff of the famous swimming family.

Before the brawl interrupted the boxing, Goodwill Games gold medalist Arthur Johnson became the third American to advance, stopping Corey Burton of Canada 2:30 into the second round of their 112-pound preliminary bout. Johnson will meet Cuban Adalberto Regalado Monday, Regalado advancing with a 4-1 decision over Simon Morales of Colombia.

Two other Americans have already advanced: world champion Kelcie Banks meets Cuban Arnaldo Mesa in a quarterfinal bout Sunday, and Andrew Maynard of Cheverly, Md., will meet Cuban world champion Pablo Romero in the semifinals Thursday.

Johnson, a junior at the University of Minneapolis, spent the first round sizing up Burton, an awkward southpaw. In the second round he wasted no time, bloodying Burton's nose with a series of lefts. Burton took an eight count with 1:35 to go in the round after Johnson delivered two big lefts and three rights, and with 1:06 to go the fight was halted briefly while he toweled off his nose. The second count came with 38 seconds to go as Johnson rained combinations on his head. When the count ended, so did the bout, the referee stopping the contest.

In wrestling, U.S. freestyle wrestler Kenneth Chertow forfeited his match for arriving late and was disqualified.

Chertow, who wrestles in the 125.5-pound class, was warming up in another area at Nicolson Hall when called for his bout against Ecuador's Galo Legarda. Chertow, from Huntington, W.Va., did not hear the first two calls. He ran to the mat after the third call, but arrived too late.