A Yale prank during a football game with Harvard will have both sides talking for years.

In a ruse for the record books, 1,800 fans at the 121st annual Harvard-Yale football game November 20 waved colored paper to spell out a message of support for the Crimson. Now that they know what they were actually spelling, however, that’s the color of their faces, too.

Dressed in “Harvard Pep Squad” shirts with red war paint on their faces, a team of 20 Yale students, led by seniors Michael Kai and David Aulicino, took over the opposing side of the Harvard Stadium bleachers, cheering and handing out white and red construction paper. They told the home fans they would be spelling “GO HARVARD.”

But the papers were actually arranged so that when waved, red letters on a white background would spell out a different message: “WE SUCK.”

Most Harvard fans were unaware that they inadvertently insulted their alma mater. The moment has been captured for posterity, however, and is now being publicized on the pranksters’ Web site, Harvardsucks.org.

The photo on the site shows the fans spelling the words out of individual pieces of paper, with the Harvard football team on the sidelines looking up at the stands, bewildered.

While the message was in full view of the Yale side, Harvard “never found out until we put the Web site up,” Mr. Aulicino claimed. “We pulled it off too well,” he allowed.

During the game, the pep squad, cheering wildly for Harvard, had the fans put up the papers for the first time 11 minutes into the game, and again with 4:47 left in the second quarter.

“We had more Harvard spirit than any Harvard student ever had,” Mr. Kai said.

The prank in this year’s season-ending Harvard-Yale game wasn’t without precedent. In the 1982 Harvard-Yale game, students from a third elite university, the Massachusetts Institute of Technology, tricked fans in the Harvard bleachers into holding up letters that spelled “MIT.”

At first, Mr. Kai and company weren’t aware of that stunt, but once they heard about it they were even more dedicated to going down in prank history. “If they could pull it off, we could pull it off,” Mr. Kai said. Still smarting from the last time, one Harvard partisan stopped the imposters and asked if they were from MIT.

The Yalies had tried their stunt during last year’s Harvard-Yale matchup, but they were deterred when security became suspicious during a pregame evacuation of the stadium as a result of a bomb scare.

This year, lessons learned, the pranksters arrived at the game – the two Ivy League colleges call it “The Game” – with their convincing pep squad outfits, for one last chance to succeed before graduation.

A video on the Web site shows the pranksters plotting out their tactics, trying on their red T-shirts, and even interviewing unsuspecting Harvard alumni in the stands, encouraging them to express their opinions about Yale.

The spirited rivalry between the schools continued during halftime, with a revival of the age-old flag-stealing tradition. A Yale student decoy ran onto the field waving a Yale flag to distract authorities as another Yalie stole Harvard’s flag before being tackled by security.

A Yale senior and pep-squad member, Yoo Sun Cheong, said she thought it hurt Harvard most that the prank was done on their home turf.

“It was fun to be in enemy territory,” another participant in the prank, Ella Smith, said.

“We did this for Yale because we love it here,” Ms. Cheong said yesterday from New Haven.

Harvard students, however, have not attempted retaliation, so far as is known. Mr. Kai said it’s because they’re no fun. Said Ms. Cheong: “We don’t think Harvard is going to be able to think of anything.”

At Harvardsucks.org, $10 posters featuring a photo of the prank are offered for purchase. The proceeds, the site’s designers said, will help defray the cost of all that construction paper. They hope to break even.

Harvard officially reacted to the prank with tolerance.

It was “all in good fun,” the school’s director of athletic communications, Chuck Sullivan, said yesterday.

Besides, the Harvard camp was still gloating over its team’s victory over Yale. The win was “very special to our players and our coaches,” Mr. Sullivan said, pointing out that the game marked the first time since 1922 that Harvard had four consecutive victories over Yale. The Crimson defeated the Bulldogs 35-3, capping a 10-0 season.