Why are athletes kneeling during the national anthem? Here's what you need to know.

Anyone who's tuned in for a nationally broadcast sporting event in the last few weeks — or attended a high school or college football game — likely noticed that not everyone on the field has been obeying the announcers when they say to "please stand for the singing of our national anthem."

Those watching NFL games have seen players from the San Francisco 49ers, the Denver Broncos and the Miami Dolphins participate in protests during the anthem. And yet, after weeks of media coverage, some spectators are still asking: "Why do athletes continue to kneel during the 'Star-Spangled Banner'?"

In August, San Francisco 49ers quarterback Colin Kaepernick announced his decision to sit down or take a knee during the national anthem to call attention to police violence and injustice in black America. His act of protest followed several high-profile fatal police shootings of black men this summer — including the deaths of Alton Sterling and Philando Castile in July.

Kaepernick's act of protest has spread not only across the NFL, but even to high school sporting events. Instead of standing with their hands resting over their hearts, several athletes of color are either sitting down or taking a knee and raising a clinched fist in protest of police brutality and racial inequities; many others are joining the protests to show solidarity with their teammates, who risk public backlash and are being ostracized for peacefully exercising their freedom of speech.

Kaepernick's protest was perhaps influenced by the Black Lives Matter movement, which, through a coalition, has called for radical changes to improve the futures of African-Americans and to end the epidemic of state-sanctioned violence in their communities.

"When there's significant change and I feel like [the American] flag represents what it's supposed to represent, [and that] this country is representing people the way that it's supposed to, I'll stand," Kaepernick said on Aug. 28.

Data backs up his concerns. For decades, the modern U.S. criminal justice system has proven to be consistently unfair and deadly for black people. African-Americans are 30% more likely than whites to be pulled over by police, as well as three times more like to be searched, twice as likely to be arrested and twice as likely to be shot by a law enforcement officer, according to studies recently cited in a speech by President Barack Obama.

The quarterback's stance has been widely criticized. But it's very likely that kneeling during the national anthem will become a fixture of sporting events for the foreseeable future, given the slow speed of racial progress in the United States.