In an act of protest, San Francisco 49ers quarterback Colin Kaepernick sat through the national anthem before his team’s football game Friday, setting off a firestorm of criticism — and once again highlighting the National Football League’s complicated relationship with patriotism and the U.S. military.

Kaepernick said he was sitting out to stand up for minorities he says are oppressed across the country, citing widely reported instances of police brutality. His stance has led to accusations that he is disrespecting the United States as a whole, and troops and veterans who have served in combat specifically.

Retired Army Lt. Col. Kelly Crigger accused Kaepernick on Monday in an open letter on the veterans site We Are The Mighty of offending “99 percent of the 324 million Americans who have nothing to do with the issue you’re protesting.” Kaepernick should protest “the right way” by funding scholarships for minorities, donating football equipment to inner-city schools or writing about the problem, Crigger said.

“You’re not a freedom fighter leading your people out of bondage,” Crigger wrote. “You’re an ill-informed athlete who’s only fanning the fires of racism by sitting on the sidelines for a principle that you only understand through a simplistic pop narrative that’s little more than a hashtag campaign.”

A number of NFL players shared similar sentiments, accusing Kaepernick of disrespecting U.S. troops or worse. Minnesota Vikings guard Alex Boone called his decision “shameful,” while former Houston Texans quarterback T.J. Yates tweeted that “it blows my mind how many people hate the country they live in,” before later deleting the message.

But the NFL’s relationship with the military and patriotism is complicated, and it includes the controversial exchange of money between the Defense Department and the NFL for patriotic tributes.

Notably, a Senate report detailed last year how the Defense Department had paid at least $6.8 million for what’s known as “paid patriotism,” in which tributes to the troops were carried out at sporting events in exchange for money. The efforts ranged from members of the military singing the national anthem to the unfurling of large American flags on the field. The Atlanta Falcons alone received $879,000 over four years, while the New England Patriots got $700,000 and the Buffalo Bills received $650,000. The practice was discontinued after it was exposed.

Kaepernick’s critics have criticized him by comparing him to a few NFL players who went on to serve in the military, but those efforts have often distilled complicated stories down to a few talking points.

In one example, detractors drew attention to the story of Glen Coffee, who played with the 49ers in 2009 and went on to serve in the Army. A meme widely distributed over the weekend on social media said Coffee “gave up millions of dollars and an NFL career to serve his country,” but he actually told The Washington Post in an interview last summer that he stopped playing football because he didn’t find it rewarding, had “no clue” what he was going to do afterward, and enlisted in the Army a couple of years later.

While the meme asks “Who’s the real hero?” and former Red Sox pitcher Curt Schilling called Coffee’s story a “legend” on Twitter, reality suggests that Coffee’s career was more complicated: He was discharged in May as a private first class — indicating he was demoted at some point. He initially joined the Army to become a Green Beret, but he washed out of the qualification course and left the military without deploying after serving three years and four months, less than the typical four-year contract.

Attempts to reach Coffee through Facebook and phone numbers listed for him were unsuccessful Monday.