Recently many players in the NFL have made the choice to protest inequality by not standing for the pledge of allegiance before games.
It is normalized by society to stand when the Pledge of Allegiance comes on. As an athlete in the National Football League you are pushed into the spotlight on prime time TV, so when athletes make the choice to not come out of the locker rooms or to sit during the pledge it is bound to spark debate. Regardless, the First Amendment can be a tricky subject in situations such as this one.
As professional athletes you are not necessarily protected 100 percent by the First Amendment considering the athletes are part of a private company, the NFL in this scenario, so anything they do can be a punishable offense.