The Cool Thing to Wear to the Big Game? Something Old.

The team store: A glorified souvenir shop at stadiums and arenas, where sports fans shop for official jerseys, snapback hats and a variety of magnets and key chains.

Also: rather passé.

“That is very out,” said Lily Shimbashi of Sportsish, a pop-culture newsletter and podcast aimed to female sports fans. “No one is buying apparel from the teams anymore, because it’s boring. It’s ugly.”

For more and more fans, official game-day apparel has been replaced by less official, trendier gear sold online. This shift has created a particular frenzy around vintage sportswear, like graphic tees circa 2001 — the Mets opening day or the Florida A&M University homecoming — or colorful, crispy N.B.A. Starter jackets.

According to Google Trends, search interest in vintage N.F.L. items has nearly quadrupled in the last year, particularly in Missouri, home of the Kansas City Chiefs. The day after it was determined that Kansas City would play the San Francisco 49ers in the Super Bowl, eBay searches for vintage 49ers T-shirts rose by more than 400 percent in the United States and Canada.

But this is not just about the Super Bowl: In the last six months, searches on Etsy for vintage football jerseys, regardless of the team, increased by 62 percent, compared to the same time period last year.

“People want to wear something more unique,” said Michael Spitz, the owner of Mr. Throwback Vintage, a shop in the East Village that specializes in sports merchandise from the 1990s. “They don’t want to wear current clothes that anyone can buy at any sports store or stadium.”

Mr. Spitz, a basketball-jersey collector, has been in business in New York for more than 11 years. “Every year, vintage sports apparel has gotten harder and harder to get,” he said.

At Westside Storey in Kansas City, vintage Chiefs sweatshirts were priced around $25 when owner Chris Harrington added them to his inventory six years ago, he said. Today, some of his sweatshirts sell for more than $300.

Explaining this inflation, Mr. Harrington said that the team has improved considerably, driving up demand, while supply has dwindled. There wasn’t much supply to begin with. Much of today’s popular vintage sportswear comes from the 1980s and ’90s. And back then, Mr. Harrington said, the Kansas City team didn’t make much merch, catering to a smaller market compared to the New York Giants or Jets.

The vintage clothing trade has become more competitive, too, in every category from concert tees to red carpet looks. When it comes to team merch, there is also an abundance of “vintage-inspired” T-shirts and “retro” sweatshirts — imitations and fakes — being sold online.

“You can take off a tag and wash it a few times, and 75 percent of people that aren’t familiar with vintage are going to think it’s vintage,” Mr. Harrington said.

Then came Taylor Swift. In December, she wore a sweatshirt from Westside Storey while cheering on her boyfriend Travis Kelce. Half red and half black — a color combination that the average Swiftie could probably spin into an album-release theory — with big capital letters sprawled across the chest, the piece cost $250. Of course it made headlines.

Westside Storey sells its vintage Chiefs clothing online in twice-monthly batches, which are announced on Instagram. Before Taylor (B.T.), only about 60 percent of a drop would sell out, with each attracting 30 to 50 active visitors to the website, Mr. Harrington said.

After Taylor (A.T.), drops have typically sold out within 10 minutes and have drawn some 1,200 to 1,500 visitors to his site, he said.

At Mr. Spitz’s store in the East Village, Ms. Swift also “has changed the game and helped sales increase,” he said. “There’s always a demand for any team in the Super Bowl, but obviously there are so many new fans today because of Taylor Swift.”

Sarah Chapelle, who runs an Instagram account dedicated to cataloging and analyzing the pop star’s style — a book is coming in October — said in an email that Ms. Swift’s fans appreciate how her game-day choices “center her excitement and support as spectator but don’t act as an outright billboard for the latest merch.” Ms. Chapelle wrote that the singer opts for “small businesses that are often local to Kansas City, women-owned, handmade or offer sustainable choices like vintage.”

An old sweatshirt can never just be an old sweatshirt for Ms. Swift. It is a statement of values.

While it is true that vintage pieces appeal to young, sustainability-minded consumers, Ms. Shimbashi said, they’re also seen by these shoppers as rare and precious artifacts. That may explain their acceptance of a $200 price tag on a cotton sweatshirt.

“People want a unique way to be a part of a team’s legacy and history,” Ms. Shimbashi said.

“If you have a grandpa or grandma who is a sports fan, and they have a piece from when they were growing up, that is something you have to get your hands on,” she said. “That is so valuable right now. I have my dad’s leather Knicks jacket from back in the day, and I will hold onto that forever.”