N.F.L. fans will first see the ads on Fox on Sept. 10 just before kickoff in the network’s games on the regular season’s opening weekend, and Mr. Shanks said they were also being offered for the World Series and other “marquee events.” The network is working to integrate them sparingly into some in-game breaks with 15- and 30-second spots; it may also place them through new formats, like in a box adjacent to players on a field during pauses. The hope is that they will eventually help reduce the overall commercial time that people sit through.

“So, for example, if a pitching coach comes to the mound just to have a conversation and you know that conversation is going to last 30 seconds, is a six-second unit in there going to add to the experience and then be able to decrease the amount of ad inventory somewhere else?” Mr. Shanks said.

The effort underscores the new strategies that broadcasters are deploying to keep the attention of consumers who often clutch a smartphone or tablet — or both — while watching their shows, or avoid ads entirely through Netflix. It’s a major shift from the typical spots that TV networks sell and will put a new burden on marketers to not only attract viewers’ attention but also pitch a product in less time than it takes to read this sentence out loud.

On network television, the trend has been toward shorter commercials: In the first half of this year, 36 percent of national TV ads were 15 seconds long while 49 percent lasted 30 seconds, Nielsen data shows. In 2014, 29 percent of ads were 15-second spots, while 61 percent were 30 seconds long.