Many of the NFL players who took part in the national anthem protests that overshadowed this year’s football season were among the league's top-paid athletes, a study shows.

The players who either took a knee, sat down or raised a fist during the playing of "The Star-Spangled Banner" made an average of $3 million more in guaranteed salary than those who didn’t, the Cincinnati Enquirer reported.

The study was conducted by a 70-student sports and politics class at the University of Cincinnati.

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The Cleveland Browns team stand and kneel during the National Anthem before the start of their game against the Indianapolis Colts. (Thomas J. Russo-USA TODAY Sports)

It showed that players selected in the earliest rounds of the NFL Draft, who will likely make more money throughout their careers, had a higher likelihood of protesting — with first-round picks being three times more likely than those drafted in the seventh round.

David Niven, the political science professor teaching the course, told the Enquirer he was astonished by the findings.

“The idea in popular culture we talk about is there are two Americas – the rich and the poor. This shows there are two NFLs.”

“The idea in popular culture we talk about is there are two Americas – the rich and the poor. This shows there are two NFLs.”

— David Niven, political science professor, University of Cincinnati

The protesting players were in “a position of being on top of the NFL's inequality,” while for players who made less money, protesting became a “luxury they can’t afford,” Niven added.

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Colin Kaepernick, rightmost, began kneeling during the 2016 season to demonstrate against police brutality and racial inequality. (AP)

The students looked at 2,197 NFL players who were part of a 53-man roster for at least one game during the 2017 regular season. Their research found that 317 players had protested the national anthem.

In his annual Super Bowl address Wednesday, NFL Commissioner Roger Goodell said a possible rule that would require players to stand for the national anthem would have to be discussed during the offseason, the Record of Bergen County, N.J., reported.

A group of owners and players representing the NFL were planning to meet and address inequality and social issues within 30 days, Goodell said.

Goodell’s comments came after President Donald Trump alluded to the issue Tuesday in his State of the Union address.

The University of Cincinnati's study is ongoing and has yet to be published.