Newsstand readers of Marie Claire will see what might seem like an unexpected advertiser smack in the middle of its big September issue -- the NFL.

The magazine is publishing a 16-page insert called "The Savvy Girl's Guide to Football" -- subscribers will get it as a separate supplement -- with six ad pages for the NFL's women's apparel line. Actress Minka Kelly, who some readers will know from her role in NBC high school football series "Friday Night Lights," appears on the front. Another ad page for the league appears in the main issue itself.

The guide is a continuation of the NFL's four-year-old effort to increase its appeal to women and sell them licensed NFL apparel. The campaign began with print and TV media buys and has evolved to include point-of-sale marketing and "style lounge" retail areas inside NFL stadiums. The NFL is working with seven other women's magazines, including Vogue, Cosmopolitan and Us Weekly. But the Marie Claire effort is the centerpiece of the NFL's print campaign this year, the companies said. They declined to disclose the spending involved.

The NFL is not one of the usual suspects in Marie Claire's pages. "What's really exciting about this is who the advertiser is," said Nancy Berger Cardone, VP-publisher and chief revenue officer at Marie Claire, part of Hearst Magazines.

The NFL last advertised in Marie Claire in 2010, when it bought two ad pages, according to Ms. Berger Cardone. Additional NFL apparel ads will appear in Marie Claire's October issue.

The NFL says its female fans have increased sharply in the last decade. More than 50% of women say they watch regular season NFL games, according to Sports Business Daily, and the audience for the Super Bowl has gone from 14% female in 2002 to 46% in 2012.

As its female audience has grown, so too has the NFL's apparel business for women. Twelve years ago the philosophy around women's apparel was to "shrink it and pink it," said Ms. Bleczinski. Now the league offers a range of clothes and accessories for women and says it is increasing its marketing spending on the area this year.

Last year, a spokeswoman for the NFL told AdAge that women's jerseys were the league's fastest-growing consumer product business, marking double-digit growth over the last 10 years.

"We have female fans who know the game better than guys," said Tracey Bleczinski, VP-consumer products at the NFL. "Others enjoy the social connectivity of the game. We need to go out to our female fans. We can't wait for them to come to us."

The guide represents the increasingly collaborative relationship between the editorial and business sides of publishing. The editorial team at Marie Claire produced the content, which includes tips on hosting a Super Bowl party and a guide to "quarterback bromances," on its own. But the magazine wouldn't likely have dedicated so many pages to football without a sponsor, Ms. Berger Cardone said.

Informing readers about the upcoming football season makes sense all the same, she added. "Marie Claire readers are very much a part of the NFL's demographic," Ms. Berger Cardone said. "And football is very much a part of popular culture."

Talks about a potential partnership began in earnest last November. During a luncheon at Hearst Tower, Ms. Berger Cardone told members of the NFL front office in attendance that Marie Claire wanted to be "the female voice of the NFL."

The NFL, meanwhile, had planned to ramp up the advertising around its women's apparel.

"When we were planning for the season we went out to the different publications for the season and said we like advertising with you but it's time to evolve and truly partner," said Ms. Bleczinski. "Marie Claire came back to the table with something really unique and interesting."

As part of the campaign, Marie Claire will distribute 15,000 additional copies of the insert in the NFL's "style lounge" retail areas at stadiums.The program also includes a digital component with dedicated tweets.

Marie Claire's September issue, which is reaching newsstands this week, is the largest in the history of the publication with 246 ad pages (excluding the six from the insert), a 13.5% increase over last year. Through August, ad pages were essentially flat for Marie Claire, slipping 0.5% from 2012.