“Fantasy football is the gorilla,” says Glazer. “The devoted fan is hooked, and now the marginal fan is much more involved. To me that spells limitless potential for this business.”

According to F.T.S.A. president Jeff Thomas, there are three main reasons for fantasy football’s growth: the appeal of delving into football stats, plain love of the sport, and prize money—league winners usually win cash. Also, fantasy football can bring extra drama and excitement to watching your team on Sunday afternoons (and Monday nights), not to mention something extra to talk about at the office.

On the plus side for the N.F.L. and the TV networks: Fantasy football players have a stake in games that might otherwise have little meaning to them. This generates more buzz for each matchup, so a New York Jets fan might end up caring deeply about a contest between the Seattle Seahawks and Jacksonville Jaguars.

“Players really don’t have team loyalty anymore, so why should the fan?” says Dave Cella, president of Payday Sports, a Wilmington, Delaware, company that conducts fantasy drafts and leagues with entry fees ranging from $25 to $10,000 a team. He says his business is growing by leaps and bounds. “If anything, playing fantasy football brings you closer to the action because you literally care about every single game.”

Who’s playing fantasy football? According to F.S.T.A., 92 percent of players are male professionals who spend at least three hours a week managing their teams. About 77 percent are married with annual incomes of more than $76,000. More than half started playing offline, says the organization, which has funded market research into the phenomenon for the past five years.

Even women, long on the football-watching sidelines, are starting to find the fantasy version appealing.

“I love it competitively and as a way to follow the game much more closely,” says Katie Hofmann, a 23-year-old law student and part of a 12-team league last season at the New York law firm Dewey Ballantine. “Fantasy football makes every Sunday an event.”

Glazer, the frenetic football aficionado with the ever-buzzing cell phone, is convinced that the fantasy frenzy is still early in the first quarter.

“The interest is endless. I have restaurant managers calling every week asking who is hurt and who isn’t,” he says. “There isn’t that much I can tell them. But I better get a reservation when I need it.”

Fox Sports chairman David Hill agrees that the fantasy football angle has to be considered during an N.F.L. game, but only up to a point. “My sense is the fantasy element of our telecasts has gone as far as it can,” he says. “You don’t want to alienate the true fan.