A fan sits behind a sign referring to former 49ers quarterback Colin Kaepernick in the second half of the Redskins-Ravens preseason game at M&T Bank Stadium last month. (Rob Carr/Getty Images)

The National Football League knows that last season's national anthem protests by quarterback Colin Kaepernick and other players turned some fans away from the sport. While the number may be a small percentage of overall fans, the league has grappled with how to approach the issue and the effect anthem demonstrations have had on its fan base.

A nationwide poll conducted by The Washington Post and University of Massachusetts Lowell found 19 percent of professional football fans say their interest has decreased in recent years. Among that pool of fans, 24 percent stated, in response to an open-ended question, that political issues had made them less interested in the sport, including 17 percent specifically citing the anthem protests or Kaepernick. That compares with 7 percent who mentioned injuries or violence in the sport as the reason they lost interest.

[Read The Post-UMass Lowell poll results| How the poll was conducted]

“If you look at some of the reasons NFL viewership was down last year, that is a reason that’s mentioned by a fair amount of viewers that is something they don’t find attractive or they don’t find compelling in coverage of the football game,” CBS Sports Chairman Sean McManus said. “How big a factor it was, I don’t really know. But it was one of the factors that I think perhaps led to the slight decrease in ratings last year.”

In the new poll, conducted the week of Aug. 14 among a random sample of 1,000 adults, those who said the insertion of politics made them less interested in pro football make up just 4 percent of football fans. And in the general question about football interest, about as many fans say they have become more interested in the sport, 23 percent, as say their interest has waned, with a 58 percent majority saying their interest is unchanged.

Still, many powerful figures within the NFL have reacted with alarm over the effects of the anthem demonstrations, which Kaepernick began last fall to call attention to police mistreatment of blacks and other minorities. While Kaepernick has not been signed by an NFL team, some players have staged anthem protests in support this preseason.

Dallas Cowboys owner Jerry Jones said he does not want his players protesting. Baltimore Ravens owner Steve Bisciotti solicited fans' opinions before declining to pursue Kaepernick when his team needed a backup quarterback.

Among sports fans, the Post-UMass Lowell poll finds 64 percent say players speaking out on political issues such as Kaepernick’s protest is a problem, 36 percent labeling it a “major problem” and 28 percent viewing it as a “minor problem.” Of nine potential NFL problems tested in the poll, political speech by players ranked sixth. By comparison, player health problems caused by head injuries were deemed a problem by 90 percent and a “major problem” by 76 percent.

There are also fans on the opposite side of the debate. In late August, a dozen activist groups gathered outside of the NFL's offices in New York to protest Kaepernick's continued unemployment, and some fans have stated they will boycott NFL games because of their belief Kaepernick has been denied a job over his actions.

The league office has provided teams with no explicit mandates or official guidance on how to approach players protesting, according to league officials.

“And I might make the case that it’s the smartest thing they’ve done,” said one high-ranking NFL team executive, who requested anonymity to speak freely about a controversial topic. “If they did try to offer guidance, it would get leaked in about five seconds, so I give them credit for not having done that. . . . You do worry about it, but when it gets right down to it, I don’t think it’s going to — I think you just let it fade away on its own.”

NFL Commissioner Roger Goodell, often heavy-handed in matters of player conduct, has been open publicly to letting players express their political views.

“The national anthem is a special moment to me,” Goodell said last month in a meeting with Arizona Cardinals season-ticket holders. “It’s a point of pride. That is a really important moment. But we also have to understand the other side that people do have rights and we want to respect those.”

Many players have felt inherent pressure not to protest in order not to risk non-guaranteed contracts. Even those who oppose protests believe they will not undermine the league’s popularity in the long run.

“Ultimately it might [tick] some people off, but does it get to the core of affecting the league? I don’t think so,” the executive said. “But maybe I’m seeing it through glasses that are too rose-colored, I don’t know. . . . I think it’s just going to fade away, and if they do go out and do that, and then I think it’s probably a positive for a league because it’s our players working to make the country a better place.”

Lenny Miller, a 42-year-old from Brunswick, Ga., said he used to watch as many NFL games as he could. Now he watches only college football, refusing to partake in the professional game after Kaepernick and others demonstrated during the national anthem.

Miller said he believes players should protest if they choose and agrees that some Americans are oppressed and criminal justice needs reform. But he will not watch the NFL as long as the protests happen on the sidelines in front of the flag.

“We got soldiers dying, and we got millionaires protesting our flag before they play a game,” Miller said. “I have a major problem with that.”

If the protests cease, Miller would happily revert to being an NFL fan.

“Absolutely,” Miller said. “I love football.”

This Post-UMass Lowell poll was conducted Aug. 14-21 among a random national sample of 1,000 adults reached on cellular and landline phones. The margin of sampling error for overall results is plus or minus 3.7 percentage points; the error margin is 4.7 points among the sample of 598 football fans.

Emily Guskin contributed to this report.