Last updated on .From the section American football

Colin Kaepernick has not played in the NFL since March when he opted out of his San Francisco 49ers contract

"This is what lynchings look like in 2016."

A video accompanies Colin Kaepernick's Instagram post. It begins as two white police officers wrestle a black man to the floor.

One officer appears to cuff the man's hands behind his back. Another, positioned by the man's shoulders, tightly presses his head to the ground.

The same officer moves one hand away, reaching for his gun. He points it to the man's chest, and fires.

Alton Sterling, 37, died of gunshot wounds to the chest and back.

Former San Francisco 49ers quarterback Colin Kaepernick first protested against racial injustice and police brutality by kneeling down during the United States national anthem in the summer of 2016. Since then, a whole movement has grown around that gesture.

BBC Sport's Richard Conway, David Lockwood and Simon Clancy travelled to the US to investigate. Listen again to BBC Radio 5 live's programme, On Bended Knee, and watch a special Newsnight report.

"Another murder in the streets because of the colour of a man's skin, at the hands of the people who they say will protect us," Kaepernick writes.

"When will they be held accountable?"

The next day, 6 July 2016, another black man is shot dead by a police officer.

Philando Castile, 32, is shot seven times during a traffic stop. He died in the driver's seat with his girlfriend beside him and her four-year-old daughter in the back.

Police dashcam footage shows officer Jeronimo Yanez firing several times into the car. He pulled it over because of a broken brake light.

Police dashcam has been released of the Philando Castile shooting

The microphone on Yanez's uniform picks up this exchange:

Yanez: "You have a licence and insurance?"

[pause]

Castile: "Sir, I do have to tell you I have a firearm on me."

Yanez: "OK, OK. Don't reach for it then. Don't pull it out."

Castile: "I'm not pulling it out."

Yanez: "Don't pull it out."

After the shots were fired, Castile's girlfriend Diamond Reynolds took out her mobile phone and livestreamed from inside the car as the officer screamed for her not to move.

"Please don't tell me my boyfriend just went like that," she says.

"Please officer don't tell me you just did this to him. You shot four bullets into him, sir. He was just getting his licence."

Reynolds is handcuffed and held in the back of a police car with her daughter, who says: "Please stop cussing because I don't want you to get shooted. I can keep you safe."

'I don't want you to get shooted': Inside police car after Castile shooting

Thursday, 7 July 2016.

A black former member of the US Army Reserve kills five police officers as a Black Lives Matter march is held in Dallas. The march was organised to protest against the shootings of the previous two days.

Micah Johnson, 25, is himself killed following a stand-off with police, who sent remotely detonated explosives into the car park where he had taken refuge.

The city's police chief David Brown reveals Johnson told a negotiator he had wanted to kill white people, especially white police officers, because he was angry about the recent shootings of black men by police.

He is said to have shouted: "How many did I get?"

A step-by-step guide to Dallas shootings

'A very deep thinker'

The tattoo across his chest reads: "Against all odds."

Kaepernick was adopted, a mixed-race baby raised by a white family. The Kaepernicks had two young sons who died because of heart defects. They wanted another child.

Their boy grew up to become a superstar, and one of the most divisive figures in the United States.

At high school he was a brilliant baseball pitcher, but the NFL was his focus. He could throw the ball. A quarterback.

Kaepernick posted this photo with his mum Teresa with the caption: "She showed me how my heart was supposed to radiate! Love you!"

First, he had to reach the college game. It wasn't easy. Scouts from the University of Nevada - the only one to eventually offer him a scholarship - watched the clips his older brother had burned to DVD, but even they were not convinced.

They took a gamble because they saw him dominate a high-school basketball game he really should have missed, external-link having been struck down with fever the same day.

He went to college. He studied for a degree in business management, excelled on the pitch, and opened his curious mind wide to the world.

Dr Reginald Stewart spent 19 years at the University of Nevada, and knew Kaepernick during his time there.

He told USA Today: external-link "He is very, very smart and very intellectual. He's a very deep thinker. What he's doing is absolutely and directly in line with how he's always communicated.

"It's not like I turned on the TV and was like: 'Wow, where did this come from?' I was like, you know what, he has been thinking about these issues for at least the time I've known him. At some point, he made the decision that this was important enough for him to act."

Kaepernick is drafted by the San Francisco 49ers in 2011. He leads them to the Super Bowl two years later, but they lose to the Baltimore Ravens.

He continues to read widely - about the civil rights movement and post-colonial theory, Malcom X's autobiography and Franz Fanon's The Wretched Of The Earth.

He begins to attend classes at the University of California, Berkeley, having befriended Ameer Hasan Loggins, who is working towards his doctorate in African Diaspora Studies.

In August, Loggins wrote an article for The Athletic external-link about their relationship. He compared Kaepernick to Ella Baker, the civil rights activist who died in 1986, aged 83.

"She was a civil/human rights leader that was invested in developing a leaderful movement," Loggins wrote. "She pushed the folks to politicise and mobilise the people via group-centred leadership.

"Here I am, taking leadership cues from Ella Baker, and next thing I know I am in the inner circle of a passionate, intelligent and conscious NFL star with a tremendous heart and a righteous indignation over the treatment of the oppressed.

"I met Kaepernick before he became a cultural icon and a lightning rod for both hope and hatred.

"People that trace our connection to UC Berkeley assume he became politicised in my class. But Colin was aware, focused, well-read, eager to learn."

And then came three days in July last year.

The perilous fight

The singer pauses, hanging between verses. He knows - like the thousands standing around him in the stands, on the pitch and on the stage - that the Star-Spangled Banner, the American national anthem, is about to reach its highest point.

Kaepernick is on the team bench. Sandwiched between two giant soft-drink barrels, he sits alone as thousands roar and whoop in appreciation.

"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of colour. To me, this is bigger than football and it would be selfish on my part to look the other way," he says after the pre-season match in August 2016.

"There are bodies in the street and people getting paid leave and getting away with murder."

Kaepernick, with his shirt number slightly obscured, is by the orange drinks cart

This is not his first protest. But it is his first protest in team kit. And it is the first time he is asked about it.

His silent, solitary gesture of solidarity makes a lot of people very angry. One of those is Nate Boyer. He used to be in the US Army Special Forces and is a former NFL player.

"When I saw that, I felt like I was betrayed. It just hurt. It was extremely disgraceful for me. In my eyes you might as well burn the flag," he told the BBC.

"That was my initial reaction before I stopped and thought: 'What is he so upset about that he would want to protest the symbol of what our country stands for - which is freedom of rights?'"

Boyer decides to write an open letter to Kaepernick. And they meet.

Colin Kaepernick 'has potential to be icon' - Nate Boyer

The NFL star - in 2014 he signed a contract that would have been worth up to $126m (£95.8m) over six years - actually sends a taxi to take Boyer from San Diego to San Francisco, about an eight-hour drive along the California coast.

"I wanted him to stand - but I wanted him to stand because he feels like we are going in the right direction, like things are changing," Boyer says of their meeting.

"I wanted him to understand the implications of what he was doing, and he listened. That was important, because we are at a time when people just shake their fists instead of trying to fix something together. We reached a position of consensus."

A week later, Kaepernick protests again. This time he is joined by his team-mate Eric Reid, and both men kneel while the national anthem plays.

Boyer, (far right) stands with his hand on his heart as the anthem plays. Kaerpernick kneels with team-mate Eric Reid (left)

Boyer stands next to them. On the same night, at another match, Jeremy Lane of the Seattle Seahawks remains seated for the anthem. The movement is growing.

"It took courage for him to sit initially. It took more courage to bend his position a little bit," Boyer adds.

"I told him if they knelt I would be next to them with my hand on my heart, because I support your right to peacefully protest in this country. That is what I fought for."

'I guess that makes me a proud bitch!'

Mr Trump attacked protesting players at a rally in Alabama

In late September, two matches in to the 2017 NFL season, President Donald Trump makes a speech.

He says players who refuse to stand for the national anthem are "sons of bitches" who should be fired by their teams.

The reaction to his words could not be more divided.

There is support from many - who find the protest disrespectful - and there is condemnation from many others.

Kaepernick's mother tweets: "I guess that makes me a proud bitch!"

NBA star LeBron James describes Trump as a "bum".

Over the weekend of 24-25 September, never before had the protest of refusing to stand during the national anthem attracted such attention. Scores of athletes, managers and coaches - across several sports - performed some kind of protest or gesture of solidarity while the national anthem played before their games.

Some linked arms, some stayed in the dressing room, many knelt. Travis Kelce of Kansas City Chiefs became the most prominent white player to kneel.

"I will be proud of it until the day I die," he told BBC Sport.

"Hopefully it creates talk and creates change. It's very important for this to actually become a change in society instead of it just being a bash on NFL players for making a protest."

But players find themselves having to explain what their actions mean.

Many NFL supporters and the US public in general view the players as being unpatriotic, disrespectful of American values and/or the US military, and they agree with what Trump said.

Chiefs fans divided over players kneeling

Outside the stadiums, fans tell the BBC:

"I'm 100% against it and 100% behind Trump. I don't come out to the football games to see political views. This is not the venue for the protest. I will boo them."

"They need to respect the flag."

"The message was never about the anthem, the message is about police brutality against African-Americans and that seems to have been lost."

Eric Reid, who first kneeled with Kaepernick a year before, writes in the New York Times: external-link "It baffles me that our protest is still being misconstrued as disrespectful to the country, flag and military personnel. We chose it because it's exactly the opposite.

"It has always been my understanding that the brave men and women who fought and died for our country did so to ensure that we could live in a fair and free society, which includes the right to speak out in protest."

But Kaepernick himself is absent. Why?

'A prisoner of the moment'

Two NFL players walk into a computer game shop. It's not a joke, this really happened: external-link

Keith Marshall and Rob Kelley of the Washington Redskins were in Dulles, just outside the nation's capital, when they saw a young boy wearing Kaepernick's number seven San Francisco 49ers jersey. They complimented him on it.

In conversation, the 10-year-old Jaden explains why he is there. He has been saving up for an Xbox, and is keeping tabs on the price - he can't yet afford it.

So they buy it for him - with his grandma's permission of course.

Jaden explains external-link why he has a Kaepernick jersey.

"I liked how he wasn't afraid to show what he thought. He risked getting fired, which was a big thing. I wouldn't even do that, but he did, and I really like him for standing out.

"I don't know if people agree with it, but he just doesn't care what people say and that's inspired me and probably inspired other people."

Marshall and Kelley also bought Jaden a game - but it wasn't Madden, the official NFL computer game.

Had it been, Jaden would not have found his favourite player. Kaepernick is no longer in the game. In March, he opted out of his contract external-link with the 49ers. He is now 29 years old and a free agent. But off the pitch, he is busy.

"His family is probably able to do whatever they want, but not everybody is able to have the stuff that we have the luxury of having," said Kelley (right)

He has been donating money to various charities and projects across the United States - he has pledged to donate $1m external-link (£750,000) in total - and has helped set up an educational campaign called Know Your Rights. external-link

In late September, Sports Illustrated published a front cover on how sport has united following Trump's speech.

There was no Kaepernick there either.

He is not injured, and should still be capable of performing at the highest level. He has not spoken to the media for months. There are reports that team owners are refusing to sign him external-link - despite coaches wanting to.

NBA star Steph Curry was featured on the cover, after he said he would not accept an invitation to the White House. Trump later said Curry had been 'uninvited'.

Colin Kaepernick was not featured on the front of this month's Sports Illustrated magazine

When he was asked about Kaepernick's omission from the Sports Illustrated front cover, Curry described him as "a prisoner of the moment".

"That was terrible," he said. "The real people who are understanding exactly what's going on and who's really been active and vocal and truly making a difference, if you don't have Kaepernick front and centre on that, something's wrong."

Boyer, who was there when Kaepernick 'took a knee' for the first time, has not spoken to him for a while either - not since the Super Bowl, in February.

He says that "there was never any falling out as such", but he does worry about him "being pulled so far in one direction that there is never going to be any room to grow and really move forward".

He believes Kaepernick "may never play again" but adds: "I don't fear that, because he is in a much more important position now.

"If he is able to embrace those who disagree with him and love them, much like Martin Luther King did, then Colin has the potential to be something like that.

"He could be the face of something and really move this conversation forward - if he is willing to listen.

"It is going to take swallowing of pride and humility, but I would rather see him move into this realm than play again, because he has been quiet for a long time.

"We need you to be a part of this because you started this."

Trump comments 'inflammatory' - Kraft

Where will it end? Friday night football in 'Muck City'

Go past the Trump International golf course, past the country and polo club, past Twentymile Bend, and out into the sugarcane fields.

Welcome to Belle Glade. 'Her soil is her fortune.'

It is a small agricultural town, inland from the opulent coastal resort of Palm Beach, where Donald Trump's Mar-a-Lago residence is situated.

Belle Glade and its surrounding area is known as Muck City, population about 20,000. It is also a hotbed for American football talent.

Glades Central High School counts dozens of NFL players among its alumni

On Friday night, 17-year-old Kortney Ware was among the Glades Central Raiders lining up to face a team from Lake Worth, down on the coast. They won 50-8. Before the match, as the anthem played, Ware took a knee.

"I did it for the police brutality," he told BBC Sport's Richard Conway.

"People have got to speak up. I am tired of seeing us black people killed, especially young people. Every day somebody black getting killed for little stuff. It's tough for us black people. So we're standing up."

Some schools in the United States have vowed to punish players who refuse to stand for the national anthem.

And on Tuesday, reports suggested NFL owners, at a league meeting next week, are planning to introduce rules to force players to stand. external-link

The Raiders' coach, Jessie Hester, himself a former NFL player, says he "fully supports" the protests, and his players' right to do the same.

'I'm sick of young black men being killed'

"There are no better people to do it than stars," he adds.

"There is social injustice in this country that we need to address and the guys in the NFL have a platform. People listen to them.

"These players here will want them to continue to speak out and be heard, because that's the only way change can happen."

Ware says Kaepernick was "definitely" an inspiration, and he hopes the influence of his kneel gesture will continue to grow.

"A lot of people are doing it now. Even the managers doing it too. That's amazingly successful," he adds.

"This will lead to better things, open people's eyes. We need even more people doing what we doing. Everybody speak up. Please. It's not always about the football.

"It's supposed to be the land of the free. But it's not been free."

Additional reporting: Simon Clancy, Richard Conway, David Lockwood