That cycle of interest saw Sky Blue’s attendance triple after the return of the World Cup stars last month; the club had averaged fewer than 1,500 fans before the tournament. The bump in the players’ visibility has meant similar benefits for other clubs in the nine-team N.W.S.L., half of which have set new attendance records in the past two weeks. It also led to a lucrative new sponsorship agreement with Budweiser and national television deal with ESPN.

It also was a reminder, though, that those things didn’t exist when the season began in April, and that they can easily disappear if the league cannot stabilize and grow. The biggest barrier to fans’ attending and watching games may not be that they choose not to, but that they don’t know the league exists.

“I think the anticipation of our success could’ve been better from the N.W.S.L.,” said Alex Morgan, the United States star who plays for the Orlando Pride. “But at the same time I think they’re putting a lot of things in place now to hire people to be able to market the league better.”

The N.W.S.L. has had time to learn some lessons. Yet while it is in its seventh year — each of the previous two American women’s professional soccer leagues folded after only three seasons — it has never been on sure footing. Three teams have folded or left the league (two were replaced by new franchises), and Duffy is the third person to be in charge of the league. The living and working conditions for players at times have been far less than professional, particularly at Sky Blue, and many league players still hold second jobs to make ends meet.

“I sometimes feel like we unfairly hold our women’s sports leagues to a higher standard, in the sense that it isn’t going to happen overnight,” said Jennifer O’Sullivan, who was previously chief executive of Women’s Professional Soccer, which collapsed in 2012.

“It is a long-term play. It is not something that happens in three years, four years, five years,” added O’Sullivan, now a partner at the Washington law and lobbying firm Arent Fox.

For the long-term play to succeed, according to those who work in the league or follow it, the N.W.S.L. needs committed ownership groups that are willing to suffer losses, but there is ongoing debate about how those groups should be structured. Five N.W.S.L. teams currently have affiliations with a men’s professional team — four with a team in Major League Soccer, the top domestic men’s league — while the remaining four are independent.