For football fans, the 2017 season was one filled with upsets, dramatic game-deciding calls from referees – and politics. And it looks like 2018 will be no different.

President Trump set his sights on the National Football League when he lashed out at athletes who protest the national anthem before games.

The response from the NFL and its players was swift and unavoidable as games brought opposing teams together, united against a common opponent: the president.

Read on for a look at Trump's gripes with the sport.

Kicking off the new season

As the 2018 preseason kicked off, many players continued to protest during the national anthem – either by kneeling or raising their fists into the air. And it did not go unnoticed.

“The NFL players are at it again – taking a knee when they should be standing proudly for the National Anthem,” Trump said. “Numerous players, from different teams, wanted to show their ‘outrage’ at something that most of them are unable to define. They make a fortune doing what they love.”

“Be happy, be cool! A football game, that fans are paying soooo much money to watch and enjoy, is no place to protest,” he continued. “Most of that money goes to the players anyway. Find another way to protest. Stand proudly for your National Anthem or be Suspended Without Pay!”

The NFL released a statement on the preseason protests.

“The NFL has been engaged in constructive discussions with the NFL Players Association regarding the anthem and issues of equality and social justice that are of concern to many Americans,” the statement said. “While those discussions continue, the NFL has agreed to delay implementing or enforcing any club work rules that could result in players being disciplined for their conduct during the performance of the anthem.”

The statement went on to say that the league's national anthem policy remained unchanged: it will continue to be played before each game, and all players and team staff on the field are expected to stand for the flag and the anthem. Those who choose not to stand must remain in the locker rooms.

Trump's MVP

The league may still be deciding whether it's going to require players to stand at attention if on the field during the national anthem, but Dallas Cowboys owner Jerry Jones already knows what his team will do.

"Our policy is you stand during the anthem, toe on the line," Jones said ahead of the 2018 season.

Trump praised Jones' decision, saying his move "is what the league should do."

Jones instructed Cowboys players to stand for the anthem last year as well.

Trump benches the Eagles

Trump announced June 4 that the Philadelphia Eagles would not visit the White House to celebrate the team's Super Bowl win amid the national anthem dispute.

Trump, in a statement, said the team is "unable" to visit the ceremony because they don't agree with his belief that NFL players should "proudly stand for the National Anthem, hand on heart, in honor of the great men and women of our military and the people of our country."

The Eagles apparently wanted to send a smaller group of players — as a handful did not plan to attend — but Trump seemingly uninvited the entire team.

A group of 1,000 fans, however, are still invited to attend a "different type" of event, one which Trump said "will honor our great country, pay tribute to the heroes who fight to protect it, and loudly and proudly play the National Anthem."

Trump cheers on the NFL

After the NFL decided players should stand for the national anthem or face a fine in the future, Trump praised the league, telling Fox News the team owners “did the right thing with that.”

The league has adopted a new policy which mandates that players and personnel have to “stand and show respect for the flag and the anthem” or be fined. Those who do not wish to stand for the national anthem can stay in the locker room “or in a similar location off the field” until it’s over, the NFL said.

“I don’t think people should be staying in the locker rooms, but still I think it’s good. You have to stand proudly for the national anthem,” Trump said. “You shouldn’t be playing, you shouldn’t be there. Maybe they shouldn’t be in the country.”

Trump credited “the people” for enacting the policy change at the NFL. “I brought it out. I think the people pushed it forward,” he said.

Post-game problems

Several Philadelphia Eagles players said they would skip the customary White House visit even before Trump made the June 4 announcement.

Safety Malcolm Jenkins confirmed to a WTXF-TV reporter in May that he would not be visiting the White House. And in April, defensive end Brandon Graham reportedly commented, "as of right now, I won't be there."

Prior to their Super Bowl win, both defensive end Chris Long and wide receiver Torrey Smith -- who is now with the Carolina Panthers -- said they, too, wouldn’t attend the usual celebration at the White House should the invitation be extended.

"We are in the process of working through the logistics of a trip to Washington D.C., including a visit to the White House on June 5," an Eagles spokesman told NFL.com on May 17.

Pre-game announcement

In a Super Bowl LII presidential message, Trump spoke about U.S. service members and standing for “The Star-Spangled Banner.”

Trump said, “We owe these heroes the greatest respect for defending our liberty and our American way of life. Their sacrifice is stitched into each star and every stripe of our Star-Spangled Banner. We hold them in our hearts and thank them for our freedom as we proudly stand for the National Anthem.”

State of the NFL

During Trump’s first State of the Union address – less than a week before Super Bowl LII – Trump seemingly took a jab at those who protest the national anthem.

While acknowledging White House guest Preston Sharp, a young boy who organized a campaign to put American flags on veterans’ graves, Trump said he “reminds us why we salute our flag, why we put our hands on our hearts for the Pledge of Allegiance and why we proudly stand for the national anthem.”

Trump takes on Roger Goodell

Trump said NFL Commissioner Roger Goodell “lost control of the hemorrhaging league,” on Twitter.

“Can you believe that the disrespect for our Country, our Flag, our Anthem continues without penalty to the players,” Trump said. “The Commissioner has lost control of the hemorrhaging league. Players are the boss!”

Marshawn Lynch’s defense

After Trump publicly criticized Oakland Raiders’ running back Marshawn Lynch on social media, his mother and his coach’s wife jumped to his defense.

Trump said on Twitter that Lynch should be suspended for the remainder of the football season if he does what he did before a game: sit in protest during the playing of the national anthem but stand for Mexico’s anthem.

Delisa Lynch, the football player’s mother, fired back, hitting the president for his past failures to become an NFL team owner.

And Linda Del Rio, the wife of Raiders Coach Jack Del Rio, reportedly said on Twitter, “President Trump I voted for you, which I now regret. Football is a powerful platform – here’s the charitable work we did in Mexico City #NFLproud.” Her account appears to have been deactivated.

Pence out of the game

Vice President Mike Pence attended the Indianapolis Colts game in his home state in October – but not for very long.

Pence and his wife walked out of the game after players from the San Francisco 49ers kneeled during the national anthem.

Trump later tweeted that he was “proud” of Pence and his wife, Karen, for leaving the stadium.

Jerry Jones’ play call

Dallas Cowboys owner Jerry Jones said his players must stand for the national anthem – if they don’t want to remain seated on the bench for the game.

"I know this, we cannot ... in the NFL in any way give the implication that we tolerate disrespecting the flag," Jones said after a team loss. “We know that there is a serious debate in this country about those issues, but there is no question in my mind that the National Football League and the Dallas Cowboys are going to stand up for the flag. So we're clear."

When pressed on other signs of protest, such as players holding up a fist at the end of the song, Jones reiterated that “if there’s anything that is disrespectful to the flag, then [they] will not play.”

Cowboys gain ground with Trump

Along with Jones, the Cowboys briefly knelt together before the national anthem. But when the “Star-Spangled Banner” played, the Cowboys stood with locked arms. The Arizona Cardinals did the same.

“The booing at the NFL football game last night, when the entire Dallas team dropped to its knees, was the loudest I have ever heard. Great anger,” Trump tweeted.

“But while Dallas dropped to its knees as a team, they all stood up for our National Anthem,” he continued. “Big progress being made – we all love our country.”

Trump has said that he had spoken to Jones, calling him a “winner who knows how to get things done.” He also said athletes “will stand for our Country!”

Sarah Sanders takes a shot

White House press secretary Sarah Sanders defended Trump’s comments on the NFL and its players, saying it’s “always appropriate for the President of the United States to defend our flag, to defend the national anthem and to defend the men and women who fought and died to defend it.”

Sanders also suggested athletes protest “the [police] officers on the field who are protecting them instead of the American flag.”

Race versus respect

Trump said that his issue with athletes’ protests was about “respect” for the U.S. and not race.

“The issue of kneeling has nothing to do with race. It is about respect for our country, flag and national anthem. NFL must respect this!” he said.

Brady breaks Trump’s tackle

Despite his oft-reported friendship with Trump, New England Patriots quarterback Tom Brady said he disagreed with the president’s remarks on the NFL.

“I certainly disagree with what he said. I thought it was just divisive,” Brady said.

Game time decisions

After the president’s speech and tweets, multiple NFL teams and players decided to take a stand – by taking a knee or remaining in the locker room during the Sept. 24 games.

The Pittsburgh Steelers, Seattle Seahawks and Tennessee Titans all remained in their locker rooms while “The Star-Spangled Banner” played.

Steelers head coach Mike Tomlin said the decision was made by the team “not to be disrespectful to the anthem, but to remove ourselves from this circumstance.” However, Alejandro Villanueva, an offensive tackle and former Army Ranger, was outside when the anthem began to play and stood alone.

Multiple teams, including the Baltimore Ravens and Jacksonville Jaguars, took a knee or locked arms during the national anthem.

And while the locked arms was meant to be a display of unity among NFL players, Trump tweeted his support for the gesture.

"Standing with locked arms is good, kneeling is not acceptable. Bad ratings!" he said.

Trump tweeted a total of six times that Sunday about the American flag and protests.

Trump tackles athlete protesters

While in Alabama to campaign for a Republican special Senate election candidate, Trump took a moment to slam athletes who kneel in protest during the national anthem.

"Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say 'get that son of a b---- off the field right now, out, he's fired,'" Trump said to cheers.

“You know, the NFL ratings are down massively, massively,” Trump said as he railed against the league’s officiating on certain tackles. “A referee gets on television, his wife is sitting at home, she’s so proud of him. They’re ruining the game.”

Trump accused "those people taking a knee" during the anthem of "hurting" football and encouraged people to "leave the stadium" if just one player protests.

Buffalo Bills come up short

Before he became president, Trump owned the New Jersey Generals of the now-defunct United States Football League (USFL). Trump pushed for the league's games to be played in the fall, in competition with the NFL, and was widely blamed for the collapse of the league.

After the USFL folded in 1985, Trump unsuccessfully tried to become a NFL team owner.

Trump lost a bidding war to become the Buffalo Bills' new owner in 2014. He was outbid by Terry Pegula, 66, who reportedly paid $1.4 billion for the team.

Trump decried the NFL and the team on Twitter multiple times after losing the ownership fight.

“The [NFL] games are so boring now that actually, I’m glad I didn’t get the Bills. Boring games, too many flags, too soft!” Trump said on Oct. 13, 2014.

Fox News' Nicole Darrah and Kathleen Joyce contributed to this report.