NEW HAVEN, Conn.—Just hours before game time yesterday, police sealed off the Yale Bowl and surrounding streets to investigate a suspicious but ultimately harmless package found on the scoreboard overlooking the stadium.

The New Haven Police Department (NHPD) and the Yale Police Department (YPD) converged on the stadium just before 8 a.m. after a Yale employee noticed the package—thought at first to be a possible bomb. Police closed off Chapel Street, which runs alongside the Bowl grounds, and closed the stadium to the public before sending in a bomb squad.

Upon inspection, police determined that the package was in fact the product of a prank by as-yet-unidentified perpetrators, conjuring images of the black balloon that rose from below the field at Harvard Stadium 21 years ago emblazoned with the letters “MIT.”

“We don’t know who it is at this point,” said New Haven Chief Administrative Officer Karen Dubois-Walton. “But there is nothing that would suggest MIT.”

The device contained fireworks and a banner, both of which would have been displayed before the crowd at an undetermined point during The Game.

“It was nothing more than a prank,” Dubois-Walton said. “If it had gone off, it would have set off fireworks and a banner would have unfurled and the wording on the banner said, ‘No school on Monday.’ So it looks like it was some reference to the fact that Yale students are going home for break and Harvard students are going back to school.”

A further sweep of the stadium by officers paired with bomb-sniffing dogs turned up nothing, and the stadium was reopened at 11:25 a.m, an hour before game time.

“The good news is that there was no delay in starting the game,” said Yale Vice President Linda Lorimer.

Despite the ultimately harmless nature of the device, Dubois-Walton said the city was taking it seriously and could file charges if police determine who was responsible for the failed prank.

“There will be a full investigation,” she said. “I call it a prank, a hoax, but that doesn’t mean there won’t be criminal consequences to that prank.”

Planning for security for yesterday’s game had been ongoing for the last two weeks, with 60 NHPD officers assigned to supplement Yale’s security detail, Dubois-Walton said.

“The security we have here today was one that’s been worked on for quite a while,” said NHPD Chief Francisco Ortiz. “We are checking bags to a certain extent...we have some civilian security staff helping the police to ask folks to look into their bags, to not bring in items like glass, or other materials of that particular nature.”

It wasn’t only the pranksters who slipped by the Yale security—students said they walked into the arena without showing tickets or being searched.

“I just walked right in,” said one student who asked not to be identified. “I just smiled at the guard. They didn’t even ask me [to stop].”

—Staff writer Timothy J. McGinn can be reached at mcginn@fas.harvard.edu.