NFL ratings are down. And that's something that doesn't happen often, considering that the league has cemented itself at the top of American sports.

Ratings for the NFL's biggest prime-time games dropped about 12 percent from last year during the first couple weeks of the season. They were down in Week 3, too, including the lowest-rated Monday Night Football broadcast ever.

If you ask some people, they'll tell you it's because of recent player protests during the national anthem, like Colin Kaepernick taking a knee.

In a way, it makes sense that people would turn to anthem protests to explain the drop in ratings. Seeing the NFL take a ratings hit is unusual and so are the protests.

But there are other factors at play too.

For example, that lowest-ever Monday night rating should probably be taken with a grain of salt.

The first presidential debate, which was aired the same night, was the most-watched debate ever. That's bad news for a football broadcast happening at the same time.

Plus, political coverage as a whole has put up big numbers throughout the election cycle. It's not unthinkable that it could be cutting into the NFL's viewership a bit.

Another possible factor in the NFL's ratings slide: A lot of the games weren't as good as usual.

Several star quarterbacks were on the sidelines during prime-time games due to an injury or suspension. Plus, nearly half of the prime-time games through Week 3 were decided by 14 points or more.

Still, it's early in the season, and ratings have plenty of time to bounce back. Professional football is still the most-watched sport in the U.S. by a long shot.