The Chicago Bears lock arms during the National Anthem in the first half of an NFL preseason football game against the Cincinnati Bengals, Aug. 9, 2018, in Cincinnati.
The Chicago Bears lock arms during the National Anthem in the first half of an NFL preseason football game against the Cincinnati Bengals, Aug. 9, 2018, in Cincinnati.

As the National Football League (NFL) pre-season began Thursday night for many teams, several players continued to defy U.S. President Donald Trump and protest racial injustice during the national anthem.

Since the 2016 season, some NFL players have taken to kneeling or turning their backs to the field during the anthem. In the United States, it is customary to stand with one's hand over the heart while the anthem is played.

FILE - San Francisco 49ers' Colin Kaepernick kneel
FILE - San Francisco 49ers' Colin Kaepernick kneels during the national anthem before an NFL football game against the Seattle Seahawks, in Seattle, Washington, Sept. 25, 2016.

Yet starting with then-San Francisco 49ers quarterback Colin Kaepernick in 2016, players have taken to silent objecting the anthem, protesting perceived racial inequality in the United States — a move that has drawn the ire of several conservatives, most notably President Trump.

In September 2017, during a rally in Alabama, Trump expressed his desire for any player protesting during the anthem to be fired, referring to any player protesting as a "son of bitch."

Trump echoed those criticisms on Twitter Friday morning, urging players to "be cool."

In May, NFL team owners — several of which donated to Trump during his election campaign — approved a policy requiring players to "stand and show respect for the anthem," with players who do not do so at risk of being fined by the league. The NFL player's union said it was not consulted in this decision, and has filed a grievance against the league in the matter.

The NFL said this week in a statement it would "delay implementing or enforcing any club work rules that could result in players being disciplined for their conduct during the performance of the anthem."

Thus, as many teams took to the field Thursday for the first time since the May decision, the spotlight was on how players would react, as many questioned what, if any, action they would take during the anthem.

Miami Dolphins defensive end Robert Quinn raises h
Miami Dolphins defensive end Robert Quinn raises his right fist during the singing of the National Anthem, before the start of an NFL preseason football game against the Tampa Bay Buccaneers, Aug. 9, 2018 in Miami Gardens, Fla.

The reigning NFL champion Philadelphia Eagles opened their pre-season at home, where defensive backs Malcolm Jenkins — who has been at the forefront of the protest, although stopping his demonstrations in December — and De'Vante Bausby raised their fists in the air, mimicking a similar gesture by two black American athletes at the 1968 Olympics. Defensive lineman Chris Long, who is white, had his arm around Jenkins' shoulder.

Jenkins, along with several other Eagles players, wore shirts before the game inscribed with statistics detailing racial inequality in the United States.

"Before we enjoy this game, let's take some time to ponder that more than 60% of the prison population are people of color," Jenkins wrote on Twitter Thursday. "The NFL is made up of 70 percent African Americans. What you  witness on the field does not represent the reality of everyday America. We are the anomalies."

In Miami, wide receivers Kenny Stills and Albert Wilson both kneeled during the anthem, while defensive end Robert Quinn clenched his fist in the air.

"As a black man in this world, I've got an obligation to raise awareness," Quinn said. "If no one wants to live in unity, that's why we're in the situation we're in."

And in Jacksonville, four players — running backs Leonard Fournette and T.J. Yeldon, linebacker Telvin Smith, and cornerback Jalen Ramsey — all remained in the locker room while the anthem was played.

New York Jets Chairman Christopher Johnson said his team will not punish any player that chooses to protest, and that he will pay off any fines levied against players for doing so.

"I just think that trying to forcibly get the players to shut up is a fantastically bad idea," Johnson said in March.

Kaepernick, who remains unsigned by an NFL team, expressed his support for the participating players on Twitter. The quarterback, along with former teammate Eric Reid, has filed a collusion grievance against the NFL's owners, alleging that they had conspired to keep the two unemployed.