Forced to. These guys are paid millions. They can put their whiny baby side away for a minute during the national anthem and stand with their hand over their heart and pretend to be grateful for a country that has given them everything.
I say ban them from the league if they can't do what is asked of them. We hear over and over that a company can fire people for their public image, even not on company time. So do it NFL. Prove it's not a one way street only for anti-american causes. The data from the season before last, when the kneeling took hold, proves its bad for business.