American footballers' campaign of protests against police brutality and racism is rippling throughout the United States and sparking demonstrations beyond the National Football League (NFL).

With growing anger over right-wing US President Donald Trump's criticism of NFL players who kneel during the customary national anthem at the beginning of games, activists have targeted team owners and politicians with their own demonstrations, and high school and college athletes have also followed suit.

On Tuesday, Carl Dix and Linda Solotaire, both members of the RefuseFascism.org activist group, confronted Dallas Cowboys owner Jerry Jones at the Conrad New York Hotel lobby.

As the pair shouted at Jones and accused him of upholding white supremacy, the Cowboys owner was whisked away by his security team.

Dix, a 69-year-old African American, said he and his fellow protesters had gathered at the hotel to rally against the NFL owners meeting there.

They singled out Jones due to the owner's recent threat to bench players who protest during the national anthem.

"I told him, 'You are trying to silence and muzzle these NFL protesters is in the tradition of silencing and abusing African Americans in this society,'" Dix told Al Jazeera by telephone.

"I have no problem with players taking a knee during these protests. I haven't stood up for the flag since I was in the army nearly 50 years ago," the military veteran said.

"It really tells you something when you have a president who isn't bothered by videos of police shooting black people in the back and unarmed people, but he is bothered when someone protests by silently taking a knee during a national anthem."

Jerry meets protestors pic.twitter.com/jH0wgsuPb5 — Lindsey Adler (@lindseyadler) October 17, 2017

The incident comes as protests grow in other professional sports leagues and high school and college football leagues in places across the US.

On Friday, football players at Midland High School in Michigan, plan to hold a silent protest during the game's national anthem, according to the local M Live news site.

Also on Friday, five cheerleaders at Kennesaw State University, a college in Georgia, plan to take a knee out of sight of the stadium's audience during the national anthem. The university barred the cheerleaders from the field until after the anthem following an incident last month when the cheerleaders knelt during the song, according to local media.

In Ames, Iowa, high school band players walked out during the national anthem at the football game last Friday night.

Last month, Cedric Ingram-Lewis, 16, and Larry McCullough, 18, were kicked off their football team in Crosby, Texas, after protesting racial inequity during the national anthem. Ingram-Lewis had raised his fist, while McCullough took a knee.

'Get that son of b**** off the field'

In August 2016, then-San Francisco 49ers quarterback Colin Kaepernick sparked widespread protests in the NFL when he knelt during the national anthem to voice his opposition to police brutality that disproportionately targets African Americans.

That year alone, police killed at least 1,093 people, according to The Guardian's database, The Counted. Although African Americans comprise roughly 12 percent of the country's population, they were almost a quarter of those killed by police.

So far this year, the Killed By Police monitoring group has recorded at least 954 police slayings.

After later leaving the 49ers, Kaepernick went through the off-season and training camps periods without being signed by a team.

But the protests had already erupted, with players taking a knee during the national anthem for much of the 2016 and 2017 football seasons.

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Last month, Donald Trump elicited widespread criticism when he called for NFL owners to fire players who kneel during the anthem, accusing the athletes of disrespecting the American flag and the country's military.

Speaking in Huntsville, Alabama, in September, Trump urged NFL owners to fire any player who participates in the demonstrations:

"Get that son of a b**** off the field right now, out, he's fired. He's fired," he told a crowd at a campaign-style rally.

Trump has denied his comments were motivated by racism, but critics have levelled the accusation nonetheless.

"The issue of kneeling has nothing to do with race," Trump insisted in a Twitter post following his initial comments. "It is about respect for our Country, Flag and National Anthem. NFL must respect this!"

On Thursday, the Trump Make America Great Again Committee launched a petition, saying the "president has asked for a list of supporters who stand for the national anthem".

The petition came after the NFL commissioner this week refused to punish players who kneel for the anthem.

Issac Bailey, a journalist and interim member of the Charlotte Observer editorial board, argued that Trump's attack on the NFL was an attempt to "use the protests as a cudgel to whip up white outrage".

"Such attacks always eventually backfire after initially seeming to work," Bailey, who is also James K Batten Professor of Public Policy at Davidson College, told Al Jazeera.

"That's what the history of race and the fight for equality tells us," he added.

"The spread of [protests] beyond the NFL definitely speaks to its legitimacy, and that some high school players and students have been punished for kneeling shows that this issue is important well beyond the ranks of professional football players."

'Long history'

As NFL protests continue to escalate, Daniel Grano, a professor at the University of North Carolina, Charlotte, expects the movement to continue to grow.

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"The gesture has travelled, and that will probably continue to leak across the boundaries of the NFL," he told Al Jazeera. "I think that is historically unique."

Grano, whose research focuses on race, politics and sports, explained that there is a "long history of protest in sports, especially protests at live events".