Peter Mulroy is loyal to the University of Notre Dame’s football team, which won one for the Gipper in the 1920s and is undefeated this season as it practices for Saturday’s game against Syracuse University at Yankee Stadium.

The basement in Mr. Mulroy’s house, on Staten Island, is a shrine to the team, with banners and photographs celebrating the Fighting Irish. He talks proudly about once high-fiving Rudy Ruettiger, the former Notre Dame walk-on famous for sacking a quarterback during the final seconds of the only game of his college career. Mr. Ruettiger’s story was the basis of the 1993 movie “Rudy.”

It is no coincidence that Mr. Mulroy’s Shih Tzu is named Rudy.

It is no wonder that Mr. Mulroy’s wife, Linda, says, “I feel like my whole world revolves around Notre Dame.”

But Mr. Mulroy never graduated from Notre Dame. He did not even attend Notre Dame.

Mr. Mulroy, a retired New York City police detective, is what Notre Dame calls a “subway alum,” someone who roots for Notre Dame but does not have a Notre Dame diploma. The term “subway alums” was coined a century ago, when Notre Dame played some away games in New York. Now Notre Dame uses the term for people who aren’t graduates of the school but are involved in alumni affairs nationally, including those in places that do not have subways.