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The first game of the 2017 NFL season kicks off Thursday night at 8:30 pm ET, when the New England Patriots play the Kansas City Chiefs.

But the real game is the one between advertisers and the TV networks that carry pro football. For years, it has been a one-sided affair: Advertisers pay more money for football every year, even though ratings have stayed about the same.

Last year shows just how powerful the NFL has become: Advertisers spent a record $4.2 billion for ads that appeared nationally during regular season games, according to research firm Kantar Media. Part of the increase was due to more national telecasts, which means more ads. But per-ad prices were also up.

Ratings, however, were down sharply last year, which NFL and TV executives blamed on a variety of causes.

Why pay more for less?

In theory, because advertisers still see football games as incredibly valuable since people watch them live at a time when people are increasingly watching shows on demand — or not watching TV at all.

That theory has worked for several years: The average 30-second ad spot during a Sunday NFL game increased about 50 percent between 2011 and 2016, according to Kantar.

But if ratings don’t bounce back this year, advertisers may finally decide that pro football isn’t must-see TV, after all.

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