SAN ANTONIO — Long before a 98-year-old nun became one of the biggest stars of the 2018 NCAA men’s basketball tournament, Immaculata, a small Catholic college outside Philadelphia, won the first three de facto national women’s basketball championships.

The Mighty Macs’ titles in the early 1970s, Bill Russell’s breakout success at the University of San Francisco in the 1950s, and the presence of Villanova and Loyola-Chicago at this weekend’s Final Four are just three data points among many that prove an undeniable fact: In college basketball, Catholic schools have long punched well above their weight. The reasons stretch back a century — and, some would argue, to the New Testament itself.

“It is a real thing,” said Julie Byrne, a professor of religion at Hofstra University in New York who studies American Catholicism.

As the Final Four coincides with Easter weekend, this phenomenon is as real as ever. Half of the No. 1 seeds in this tournament were Catholic teams, as were eight of the 68 teams that made the bracket. Loyola-Chicago is named for St. Ignatius of Loyola, the founder of the Jesuits, and has Sister Jean Dolores Schmidt as its chaplain and unofficial scout. Villanova is associated with the Augustinian Order. Both are still playing.

On Saturday, Loyola, a No. 11 seed, will play third-seeded Michigan, before Villanova, the 2016 champion, faces a fellow top seed, Kansas.

Excelling in big-time college basketball sits easily at mission-oriented institutions. Sports are not only these universities’ front porch, but also the faith’s emissary.

Villanova’s president, the Rev. Peter Donohue, hosts an opening Mass for athletes every year at which he reminds them they are ambassadors for the university’s mission. “To have our charism move on,” he said, using a dogma-tinged Greek word for spirit, “the banner needs to be carried.”

The history of basketball excellence at Catholic colleges stretches back as long as the tournament itself. In its early decades, Holy Cross, La Salle, San Francisco and Loyola racked up titles; Marquette’s golden age was in the late 1960s and ’70s; the 1985 Final Four included three Catholic schools (St. John’s, Georgetown and Villanova); and Gonzaga has had an extraordinary run of 20 consecutive tournament berths, including appearing in last year’s championship game.

Catholic hoops excellence is all the more stark when one looks at college sports’ broader landscape: Of the 65 members of the five football power conferences, only two are Catholic institutions — Boston College and Notre Dame.

Theological explanations are tempting.

“Of course,” joked the Rev. James Martin, author of “The Jesuit Guide to (Almost) Everything,” “St. Ignatius of Loyola is praying for all these schools. Even Villanova.”

But there is more than just something in the holy water. Several characteristics of Catholicism in the United States, both sociological and spiritual, have helped determine this affinity; the Catholic Church’s decision not to abandon the urban poor in the United States in the second half of the 20th century, when so many other institutions did, was particularly significant.

Much of Catholic education’s historic commitment to basketball derives from demographics.

Several decades ago, many U.S. Catholics were working-class urbanites, clustered in some of the same cities — New York, Philadelphia, Chicago, San Francisco, New Orleans — in which these schools rose up.

“Many of our schools were founded to serve immigrants and the working class — Catholics unable to get into other schools,” Martin said.

In basketball, with its relatively inexpensive overhead, compact field of play and small number of participants, they found a sport that suited them. (The same was true of working-class Jews, for whom basketball also possesses a striking similarity with their religion — a prayer service and a regulation basketball game both require 10 people.)

Many of these same Catholic basketball powers field lower-profile football teams, when they do at all (Loyola discontinued its varsity program in 1930), because of the expense of a roster close to 80 players.

“Basketball was the sport they picked because it was so cheap,” Byrne, the Hofstra professor, said. “They could do it in incredibly limited space with incredibly limited equipment.”

Over time, the schools became a magnet for black players, including luminaries such as Russell at USF and the championship Loyola-Chicago team of 1963, which broke an unspoken rule by starting four black players.

Black athletes, Catholic or not, often landed at these colleges partly because they frequently played basketball for the local chapter of the Catholic Youth Organization, which was originally founded as a kind of urban, Catholic parallel to the predominantly Protestant YMCAs. The CYOs set many black players on the path toward Catholic colleges.

“As more and more ethnic Catholics moved out of cities but parishes and schools stayed put, black kids were admitted regardless of religious affiliation beginning in the ’60s,” James Fisher, an American Studies professor at New York’s Fordham University, said in an email. “Then the church turned demographic fact into theological virtue by embracing urban advocacy and racial justice.”

U.S. Catholicism taught that all aspects of life could be sacred, Byrne said, maybe even basketball.

“It’s not that sports were particularly holy, but you could see it as a holy thing to do. It could have the potential to give glory to God,” said Byrne, referencing the Jesuit phrase “ad majorem Dei gloriam, or “for the greater glory of God.”

For St. Joseph’s coach Phil Martelli, these teachings comport with the sport that he called the “greatest societal experiment.”

“In basketball, it doesn’t matter if you’re black or white, rich or poor, city or suburbs,” said Martelli, whose wife, Judy Marra Martelli, played on those three Immaculata champions. “And in the Catholic faith, you shouldn’t be measured by those things — your W-2 or what you drive. You should be measured by your character.”