Ready for some fantasy football? It's scoring big

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NFL general managers, coaches and team owners are close to making final roster cuts for the season opener on Sept. 4.

They're looking at injured players, deciding whether rookies were worth the high draft pick or if a free agent signing was a good idea.

While the locker room chatter is happening in the pros, it's also taking place among the millions playing fantasy football—part of an industry that's worth billions and growing in popularity.

"Fantasy sports are big because people love playing it," said Paul Charchian, president of the Fantasy Sports Trade Association.

"Eighty percent of fantasy players tell us they expect to be playing in a decade, and half say they will play until they die," he added.

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Scott Minto, professor of sports business at San Diego State University and a fantasy football player, likened it to March Madness—where participants pick who they think will win the NCAA college basketball title.

"Those that wouldn't normally care about who wins the NCAA title have an interest when they take part in the bracket pools," he said.

"It's the same way with fantasy football," Minto explained.

Nearly 37 million play fantasy football

An estimated 41 million people will play some sort of fantasy sports in the U.S. and Canada this year, up from 32 million in 2012, according to the FSTA.

Participation in all fantasy sports has grown by more than 60 percent the last four years with 19 percent of all males in the U.S. playing fantasy sports.

And it's big dollars. According to the FSTA, around $1.6 billion is spent across all fantasy sports on items like apps and access to pro sports packages for fantasy player tracking.

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There's also fantasy sports-related magazines and online premium content for fans to buy.

Another $1.7 billion is spent on entry fees to fantasy leagues at an average of $70 to $100 per person. While not all leagues require fees, some can go as high as $5,000 or more.

As big as the industry is, the largest fantasy draw is football. Nearly 37 million people will play fantasy football this year, or 90 percent of all fantasy players.

Basics of fantasy football

The way fantasy football works—laid out here in basic terms—participants can join a league or form one of their own. There are public leagues, with no fees, or private ones, that do require a fee to play.

There can be as many teams as a league determines but the average is around eight to 10.

There are draft days where participants pick pro players. They can begin as early as May or June before the pro season begins, or as late as a week before the first pro game.

The goal is to pick 15 to 18 individual pro players from across NFL teams for the offense, while whole defensive squads of a pro team are chosen.

During the year, and even with each game, players on the fantasy offensive squads can be switched out with reserves.

Much like the pro game itself, there are ways to get other players during the season such as a free agency pool, waiver wires and trades.

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Then it's all about watching each game and hoping your player or players have the better statistics than the other teams.

For example, if you have Denver's Peyton Manning as your starting quarterback, you want him to have the most touchdowns, passing yards and least interceptions than any other quarterback that week.

And if you have the Pittsburgh Steelers as your defensive squad, you want them to allow the least points and get the most tackles and quarterback sacks.

Just like the real thing, fantasy teams that do well enter a playoff system to crown an eventual champion. If you're in a pay-for-play league, who might win a pot of money.

Some leagues allow playing on a weekly basis with high payouts in cash.

Top players for fantasy sites

The top sties for hosting leagues include Fox Sports, My Fantasy League and FanDuel.

But FSTA's Charchian said the industry mostly comes down to a big four of ESPN, Yahoo, CBS and the NFL.

"They're vying desperately for fantasy players," he said. "There's a lot of advertising revenue for sites that have the eyeballs of players."

Ken Fuchs, vice president and group leader at Yahoo Sports, said there's a reason brands like Toyota and Snickers advertise on Yahoo's fantasy sport sites.

"As a product (fantasy sports) has a user engagement, volume of user activity and scale that are virtually impossible to match," Fuchs wrote in an email to CNBC.

Fuchs said that Yahoo fantasy players spend more than 29 billion minutes playing fantasy sports every year, with the average being 500 minutes each month.

He added that while Yahoo does not have a direct relationship with the NFL, the two have been working on Web and mobile device initiatives to distribute NFL content.

Calls to the NFL to discuss its fantasy football platform were not returned.

Loss of productivity at work

While not considered gambling, some employers are worried about workers spending too much time on their fantasy leagues. And there may be some cause for concern.

A recent survey by consulting firm Challenger, Gray & Christmas stated some $13.4 billion in lost work output in the U.S. is due to fantasy sports.

But SDSU's Minto thinks that the productivity issue is overblown.

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"People at work talk about the Oscars, or the Emmy's or spend time on Facebook, so I don't see fantasy football as a major work distraction," said Minto.

Whether fantasy sports will continue to be a touchdown with fans, FSTA's Charchian said at some point there will likely be a reverse play.

"It can't keep growing at this pace forever," he said. "But for the near future, it's going to be a great form of entertainment."

—By's Mark Koba

Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.