Sports ad network Sportgenic on Thursday launched an online ad channel focused on mixed martial arts, a sport popular among younger males that is moving rapidly into the sports mainstream.

San Francisco-based Sportgenic has 350 sports sites on its network--many of which focus tightly on mainstream sports such as tennis, golf, and running and draw about 25 million unique visitors monthly.

While sports is an attractive online category, the problem for advertisers is that outside of the big-name sites such as ESPN.com, the market for single sports remains fragmented and difficult to reach.

“In our research, market buyers would tell us that they would love to reach these people who are highly engaged. But scale was the challenge,” Sportgenic CEO Robert Tas said.

But the challenge was worth accepting because sports attracts a number of favored demographics, particularly males 18- to 35-years old.

Sportgenic offers advertisers a single conduit through which they can reach a variety of single-sport and sports fanatic sites such as tennisreporters.net and mmajunkie.com.

But large advertisers are wary of small fan sites because they lose control of where their ads are positioned. Their ads could end up next to questionable or offensive content.

So Sportgenic works directly with its site publishers, offering them merchandizing, advertising, and social networking technology free of charge.

“We invest all of our technical development in making our publishers’ sites better because we believe the power of the long tail will win with media buyers in the long run,” Mr. Tas said.

Not all ad networks are willing to go much beyond mainstream sports. WidgetBucks, a Seattle-based ad network, which on Wednesday said it received $10 million in funding, takes a more conservative approach.

“Our vertical is based on things like NFL jerseys, MLB products, golf merchandize, team backpacks, etc.,” said Dean Jutilla, marketing director of WidgetBucks. “MMA is growing in popularity but it won’t fit any of our verticals right now.”

MMA, like boxing, has some very rough edges so it was not love at first sight for Sportgenic, which has to convince large and small advertisers that their ads will not be placed near questionable content.

“We were very hesitant at first, but the passion of the fans and the off-the-charts popularity of the sport convinced us to get involved,” Mr. Tas said. “We invested some time and resources and we’ve seen it pay off.”

Sportgenic now hosts advertising on some of the more popular MMA sites including mmaweekly.com, mmaringreport.com, and mmajunkie.com. The top 25 MMA sites draw 3 million visitors per month.