PORTLAND, Ore. — It’s easy to know when it’s game day at Providence Park.

A moving mass of red shirts jams the sidewalks and sometimes spills into the streets near the stadium, stranding cars in intersections whenever the lights change. A man on a corner fans out the tickets he is hoping to sell, and police officers keep a leisurely eye on the swarms of people lined up at the entrances.

By game time, the buzz outside the stadium fades, and as the game begins on this September night, more than 21,000 people have packed into the stands for what fans elsewhere might consider an unlikely must-see event: a professional women’s soccer match.

Crowds like this one are nothing new here, though. The women’s soccer team in this city, the Portland Thorns, has seen its attendance rise in each of its five seasons, and this year, it drew an average of 17,653 fans — more than 15 N.B.A. teams, 13 N.H.L. teams and one Major League Baseball team. Providence Park will be empty this weekend, but only because the Thorns are in Orlando, Fla., to play the North Carolina Courage for the National Women’s Soccer League championship.

In nearly every way, from on-field success to fan support to profitability, the Thorns are a model of sports franchise success. Even if they do not add a second league title on Saturday, there is an argument to be made that the Thorns are the most successful professional women’s sports team in the world.