National Anthem Protests have gone on in the National Football League ever since the 2016 NFL season. This usually involves taking a knee, sitting down, or raising a fist rather than standing during the playing of the Anthem. The movement began with Colin Kaepernick (who was then a member of the San Francisco 49ers) protesting police brutality on African American citizens. Kaepernick protested by kneeling on one knee instead of standing during the National Anthem.
This movement was not fully popularized until the 2017 NFL season when teams (instead of just individual players) knelt. Some teams have protested in other ways, such as standing but locking arms in solidarity instead of the right hand over the heart. During Week 3 of the season at a rally in Alabama, President Donald Trump stated that anybody who protests the Anthem "should be fired" and thought it would be great if the NFL owners would say, "Get that son of a bitch off the field right now!"  
In the Week 3 game against the Seattle Seahawks and Tennessee Titans, both teams stayed in the locker room during the National Anthem . Many NFL fans and spectators have counter-protested the NFL players' protests by refusing to watch games on TV or refusing to attend them. Some fans of teams who knelt at home booed the protesters after the conclusion of the anthem. Others post yard signs or bumper stickers reading, "I stand for the flag and kneel for the cross."
Houston Texans' owner Bob McNair made a controversial statement during a meeting the Thursday before their Week 8 game against the Seattle Seahawks, stating, "we can't have the inmates running the prison." The following day, running back D'Onta Foreman walked out during organized practice. Even though McNair apologized for his statement, a mass majority of the Texans' players knelt during the anthem that Sunday, reportedly all but ten of the players .
In late-May of 2018, Roger Goodell and the NFL team owners approved to instate a new National Anthem policy where players can choose to take the field or stay in the locker room during the performance. However, if the player chooses to take the field during the anthem, they must stand respectfully and are not to kneel. Despite the truce (to try and appease President Trump), some NFL players, such as Malcolm Jenkins, have expressed their displeasure with this new policy .
The protests sharply declined throughout the 2018 NFL season, although players at other levels have continued kneeling .
How to Solve This
Some people have suggested that all cops have body cameras to ensure no brutality is taking place, although this probably won't happen anytime soon. Because of this, there really is no correct answer to combat this problem.
One possibility is to stop playing the National Anthem at every single football game. The problem with this is that the Conservatives (and even some Liberals) will demand the anthem be played or they will stop attending games.
Another possibility is to go with Trump's demands: fire all protesters. The problem with this is many of the best players in the NFL have knelt at least once, and the NFL would fall even more in ratings