On any other day, junior Hugh Mackay’s blasting bagpipes would have been less than welcome outside Hollis dorm so early in the morning.

On any other day, Economics Professor David Laibson might have raised eyebrows prancing in front of University Hall with smurf-blue hair and Mardi Gras beads.

And on any other day, Xavier Ayala-Vermont ’27, attired in an inflatable lion suit, would have been doomed had he summited the statue of John Harvard in the Yard waving a Winthrop House flag — right in front of the Harvard University Police.

But this was no ordinary morning.

Friday was Housing Day, the joyful annual tradition in which students from the 12 College Houses stream into the Yard in a raucous show of pride before splitting up to storm the adjacent first-year dorms and welcome those students with the housing assignments that will shape their residential life over the next three years.

So Mackay’s bagpipes barely registered over the din — bullhorns and Bluetooth speakers, cowbells and clapping — emanating from the west side of University Hall.

Ayala-Vermont got a steadying hand and even a fist bump from the HUPD.

And Laibson, co-faculty dean of Lowell House, whooped it up with his arms in the air, basking in the sort of cheers — “DAV-ID! LAIB-SON!” — that might otherwise greet a Celtics power forward.

“This is a wonderful day for the students to show their spirit and kind of shed the super-academic, super-intense [persona] and just really be fun College students enjoying a little healthy competition,” said Nina Zipser, Laibson’s wife and fellow Lowell House faculty dean, straining over the reggaeton classic “Gasolina” and the bang of a chalk-bomb party popper, which released a plume of yellow dust over the crowd.

Zipser, who also serves as dean for faculty affairs and planning in the Faculty of Arts and Sciences, applied the dye to Laibson before they marched over at 7 a.m. in “a big blue mass” with the Lowell crowd, finding Kirklandians — typically first to the statue — and Winthrop House residents, having pulled overnight statue-side shifts.

Lowell claimed the southwest stairs of nearby University Hall, with some students wielding swords and wearing chain-mail suits with the “Blue Man” House crest, others attired in flannel Lowell pajama pants.

“This is what spirit in your University and your House is all about,” said Danoff Dean of Harvard College David Deming, ostensibly dispassionate (though he betrayed his roots as a former Kirkland faculty dean by bringing bagels to the Kirkland students by the statue at 7:15).

“It’s not really about the House itself. It’s the sense of community that it builds, the things you do together with your friends,” Deming said. “You don’t get this from having some big corporate dorm where everybody lives or from living off-campus.”

When Adams House arrived, sophomore Tess Straw blitzed the yard in her own crimson-and-gold scarf and a long military dress coat loaned by the House.

The braided-gold epaulets and brass buttons of the outerwear, however, suggested that Straw’s version of John Adams had left the Continental Congress to lead a marching band or perhaps invade Prussia.

“This is fun itself, but it’s a totally different experience to be inside all these housing buildings around us right now, listening to this, knowing your House is going to come get you,” she said, drawing festive Adams-insignia acorns on the ground using a condiment bottle of dyed chalk dust.

As her fellow students hurled slogans back and forth, Straw’s friend Arthur Tao bounded over in a green bodysuit, Leverett House T-shirt, and light-up bunny ears — the rabbit mascot inspired by the hares on the Leverett House shield. The two greeted one another with smiles and goodwill.

Just then, the Mather crew stormed the Yard.

Tao raised a green vuvuzela and blasted the plastic horn in their direction with take-that might, before shrugging it off. “I know Leverett’s the best,” he said.

Regardless of the House, he added, “It’s really cool to see the School come together as a community, because that’s not always common.”

To foster more of that spirit, Housing Day was moved from the Thursday before spring break to the Friday after to relieve the stress of conflicting with midterms and to scaffold more events into a “Spirit Week” without having everyone immediately depart.

That meant not just the late-night food trucks on Thursday and the customary new-House welcome dinner Friday night, but also a dodgeball tournament followed by the second annual “Johnnies” on Saturday. The Oscars-style ceremony honors the best student-made Housing Day music videos, with winners taking home coveted John Harvard statuettes.

In this case the University founder eschews his traditional seated pose to celebrate, as the tagline notes, “videos so good John Harvard stands up for them,” said Harvard College Dean of Students Thomas Dunne, a veteran of several institutions, deeming Housing Day “the best college tradition anywhere.”

Shortly before 8:20 a.m., students started storming the dorms, and soon first-years were converging on the grass to compare notes, hugging and shouting things like, “You got Adams too?! Yeah, baby!”

First-year Olukayode Ekundare wore a big smile.

He had watched the scene from up high in Hollis with friends since 6 a.m. and was thrilled when the upperclassmen finally burst in — “jumping up and down, playing music, bang-bang-bang on the door.”

He was happy to get Currier — but had to dash. It was just past 9, and he was late for a lecture.