Almost exactly a year ago, Kristin Juszczyk, the wife of the San Francisco 49ers fullback Kyle Juszczyk, who had been happily D.I.Y.-ing her own game-day merch, became the Cinderella of her own fashion fairy tale when Taylor Swift wore one of Ms. Juszczyk’s custom-made jackets to watch her new boyfriend, Travis Kelce, play football. Before you could say touchdown, she had 1.2 million Instagram followers, a licensing deal with the N.F.L. and was chosen to make a jacket for the winner of the Indy 500.

Now she is teaming up with Emma Grede, a founding partner of Skims, the chief executive of Good American and a “Shark Tank” guest-star investor (also a woman known as the Kardashians’ “secret business weapon”), to turn her home hobby into an actual brand. Together with Fanatics, the sports merchandiser founded by Michael Rubin of White Party fame, they are introducing Off Season, a unisex collection of three puffer (but not too puffy) styles with a sort of Hilfiger-esque air: a vest, a cropped jacket like the one Ms. Swift made famous and a longer coat.

The collection, in the colors of five N.F.L. teams (the 49ers, Detroit Lions, Philadelphia Eagles, Buffalo Bills and Kansas City Chiefs), ranges in price from $295 to $495 and will be available online on Jan. 7.

With headquarters in Los Angeles, where Ms. Grede lives, Off Season is the latest example of the connections between fashion and sports, as each becomes defined as a subset of entertainment. Indeed, the holding company Ms. Grede owns with her husband, Jens Grede, is called Popular Culture, and the goal of her partnership with Ms. Juszczyk, Ms. Grede said, is to “define an entirely new category of apparel.”

They are convinced that football fan chic (and maybe soccer and baseball and more) is not an oxymoron but a market opportunity waiting to happen. So much so that they were happy to get on the phone to explain why. This interview has been edited and condensed.