Colin Kaepernick, at the time a San Francisco 49ers quarterback, began protesting the national anthem during the 2016 pre-season. He started by sitting on the bench, and then he began taking a knee.
He said he was "not going to stand up to show pride in a flag for a country that oppresses black people and people of color."
A handful of football players around the league followed Kaepernick’s lead, kneeling or raising their fists as the national anthem played. The appropriateness of kneeling during the anthem sparked debate throughout the country, and the issue drew a new round of attention when President Donald Trump began criticizing kneeling athletes.
Critics of players protesting during the anthem argue that athletes are not supposed to be political figures. But athletes have historically been front and center during times of perceived social injustice. Kaepernick and LeBron James have forebears in Muhammad Ali, Tommie Smith and John Carlos, among many others, experts say.
And yet after all these years, there is no clear picture of how protests affect sports viewership.
The latest professional sports protest came from the NFL on Sunday and Monday, with about 200 players sitting, kneeling or not appearing during the national anthem, according to an estimate by The Associated Press. The ratings for the league dropped about 6 percent compared to the previous week, but there is no clear cause and effect, experts say.
"There are so many variables when it comes to who’s watching football and certainly it is trending downward, that started before any of these protests began," said Robert Thompson, a professor of television and pop culture at Syracuse University. "I'm not saying there aren't some people who aren't watching because of these protests, there are some. But how significant it is, it's really hard to tell."
The downward trend, Thompson said, could be attributed to fans being drawn away by last year's election and news cycle, poor matchups or just the larger availability of entertainment outside of football from streaming services like Netflix. There's never been a formula as to how it works, since "it's show business, it's not science," he said.
Matthew Andrews, a sports history professor at University of North Carolina-Chapel Hill, says controversial issues tend to increase ratings, and a recent slip in the NFL's ratings is difficult to interpret because of other issues, including high-profile reports on brain injuries.
"[Muhammad] Ali spiked all of his subsequent fights after his hiatus. All of his fights were blockbusters -- and sure, people rooting to see him get his butt kicked," Andrews said. "Controversy sells tickets. Racial tensions sells tickets."
Trump made inflammatory remarks about NFL players protesting during the national anthem while at a campaign rally for Luther Strange in Alabama Friday night. He called on the 32 owners to fire any player who participates in sideline protests.
"Wouldn’t you love to see one of these NFL owners, when somebody disrespects the flag, to say, 'Get that son of a b---- off the field right now, out, he’s fired. He's fired,'" Trump said to a loud applause.
He also encouraged football fans to "pick up and leave" if they see a player kneeling.
Sports history professors from universities around the country called his remarks "unprecedented."
"Presidents and politicians tend to use sport to cultivate messages of national unity," said Frank Guridy, an associate professor of history at Columbia University. "I am certainly not aware of a case when a US President referred to fellow citizens 'sons of b------.'"
Through three weeks, viewership for national telecasts of NFL games is down 11 percent this season compared to 2016, the Nielsen company said on Tuesday.
Nielsen said the games averaged 17.63 million viewers for the first three weeks of last season, and have dipped to 15.65 million this year. However, NFL spokesman Joe Lockhart said that Monday night's game viewership was up 63 percent from last year.
Average attendance at regular season NFL games last year was the highest since 2007, when the NFL set an all-time record in attendance. The NFL says ticket sales are "on par" with last year.
Despite the loss of viewers in recent years, the NFL is still the most popular program on television. Its popularity is a reason it draws appeal for protest since protests exist to be seen, Thompson said.
Sports fan Spencer Davis watches college and professional levels of football and basketball. The wave of protests and outspoken athletes aren’t stopping him from tuning in.
"I watch because I like sports. They don't talk on the field, they play," Davis said. "If I don't want to hear what they have to say after the game I can easily avoid that. The people saying that athletes shouldn't speak about sensitive issues and stick to sports because they are celebrities are the same people that elected a reality tv star president."
Guridy noted that there is "no concrete evidence that athletic activism has deterred fans from watching sports."
"I think the long-term effect of this weekend will be to dial back the hyper-patriotism that crept into American sports after 9/11," said Daniel Widener, a history professor at University of California, San Diego. "Most Americans don't realize that [other countries’] spectators rarely hear their national anthems sung at sporting events."
The president's "son of a b----" remark was met with sharp responses from athletes and sports franchises over the weekend.
As an Air Force veteran who served nine years of active duty in Kuwait, Iraq and Afghanistan, Mitchell Moss said he "fought for that right," for athletes to protest. Moss said he hopes "more athletes take a stand" and isn't deterred from watching their games.
"Their sole purpose on this earth isn't to just entertain the masses. They are allowed to have an opinion and protest in the name of equality," Moss said. "They have the platform to be heard and keep the discussion going."
NFL's Lockhart said Monday that football should "stop playing politics" because "families and friends come together to enjoy the great game." He said for viewers to turn away for politically motivated reasons, whatever they may be, would be "unfortunate."
But Thompson contests that "The NFL is never just a game," and that "it has never been written down anywhere that a football game is supposed to be totally apolitical."
Hours after Trump criticized the NFL’s policies, he uninvited NBA star Stephen Curry to the White House for the traditional visit made by the winning team, a move Thompson called "really bizarre."
"Going to the White House is considered a great honor for a championship team.Stephen Curry is hesitating,therefore invitation is withdrawn!" Trump tweeted Saturday morning.
Curry said the way the president "feels the need to target certain individuals" is "beneath our country" and "it's not what leaders do." The team then announced their trip to the White House was canceled.
"Trump isn’t the first president to use Twitter, but he is certainly the first to use it this way," Thompson said.
Current and former NBA stars like LeBron James, Kobe Bryant, Chris Paul and Magic Johnson criticized Trump’s decision. James called the president a "bum."
"He’s now using sports as the platform to try to divide us. And we all know how much sports brings us together, how much passion it has," James said in a self-recorded video for "Uninterrupted." "And for him to try to use this platform to divide us even more is not something I can stand for and it’s not something I can be quiet about."
Widener sees James' activism as an example of the NBA's understanding of a "reciprocal relationship with" its black athletes.
"The MLB could not be more different, I doubt we'll see the same kind of activity," he said. "Professional football is caught in between. The audience crosses class and racial lines."
Guridy sees parallels between the outspoken athletes today and those of 50 years ago.
"In many ways today's black athletes are following in the footsteps of Muhammad Ali, Harry Edwards, Tommie Smith and John Carlos and other members of the 60s generation of radical black athletes," he said. "I think we are in a unique historical moment when a wider range of athletes at all levels, from youth to professional, are expressing dissent against police brutality and the recent resurgence of white supremacist politics."
Boxing legend Muhammad Ali famously refused to fight in the Vietnam War, calling it a hypocritical cause for black people to be part of.
Harry Edwards, a civil rights activist and sociologist, has dedicated his career to highlighting the inequalities black athletes experience. Edwards was also behind the Olympic Project for Human Rights, which led to the black power salute at the 1968 summer Olympics in Mexico. American track stars Tommie Smith and John Carlos raised their fists while on the podium receiving their gold and bronze medals, respectively, for placing in the 200-meter run.
Ali was barred for years from boxing, fined and jailed for his refusal to fight. Smith and Carlos were expelled from the rest of the Olympic games and were forced to return their medals.
Andrews also pointed to these athletes for their black activism, comparing it to Kaepernick's ostracized stand against the treatment of minorites in America.
"If there is a truism about American sports, it’s when black athletes speak their minds, so many white Americans get upset," Andrews said. "Statements of black athletes raise the ire of white Americans."
Trump said his opinion on athletes kneeling during the anthem "has nothing to do with race" but respect for the flag.
Some fans agree.
"We as fans watch sports to have a release from real life and turning on a game and watching a multi-millionaire kneel for the national anthem is a direct slap to the face to the millions of fans that love their country," said sports fan Brent Reed. "I, for one, have cut [football] out of my life -- that's coming from a guy that absolutely loves sports and the NFL."
Reed said other issues, including the NFL's actions in domestic violence cases, influenced his decision to abandon it.
The NFL’s national anthem protest is a potentially historic event because of the wide display across the entire league, Andrews said.
"I think we are going to be talking about this weekend 50 years from now," Andrews said. "I think we have reached some sort of tipping point. We’ll see where it goes."