At Barclays Center on Saturday, during the first half of a game between the New York Liberty and the Indiana Fever, a man on the floor level held up a sign that instructed the crowd to “get loud.” There was no need for the prompt.

Some of the raucous crowd was there to watch Caitlin Clark — the Fever’s wunderkind rookie — play her first professional game in New York City, some were Liberty fans, and more than a few seemed to be there to cheer for both sides.

There were celebrities sitting courtside, like Billie Jean King, Jason Sudeikis, Megan Rapinoe and the actress Amy Ryan. And there was basketball royalty in the building as well, including Sue Bird, Pau Gasol and Dawn Staley, the coach of the South Carolina women’s basketball team that beat Ms. Clark’s Iowa Hawkeyes in this year’s N.C.A.A. tournament final.

Every time the Jumbotron flashed one of the famous faces, the crowd seemed to get even more electric.

The building was buzzing for the Liberty’s first home game of the season, which set a franchise record by drawing 17,735 fans. And it was part of an exciting first week of the W.N.B.A. season, with many hoping the arrival of stars like Ms. Clark will usher in a more prosperous and popular era.