Network executives have long used the National Football League’s live games as a last line of defense against the rapid growth of “cord-cutting” and on-demand viewing upending the industry.

But now, the NFL is seeing its ratings tumble in the same way that the Olympics, awards shows and other live events have, falling more than 10 percent for the first five weeks of the season compared with the first five weeks of last season. A continued slide, executives say, could pose an even bigger danger: If football can’t survive the new age of TV, what can?

Football’s traditional TV audience “is never going to be what it was again,” said Brian Hughes, a senior vice president at Magna Global, which tracks audience and advertising trends.

The explosion of modern entertainment options, offered on more devices and at any time, has splintered American audiences and sped TV’s decline, Hughes said. “Sports seemed to be immune from it — it was live, the last bastion of broadcast television. But [the world] has caught up to it now.”