As an employee, you must follow the employer's directives when at work (so long as those directives are not illegal. The game operations manual DOES specify the expected behavior during the National Anthem and even appropriate actions when the behavior is not followed. There are consequences for any action whether it is in violation of the employment agreement or against societal norms. The NFL is in a tough spot by ignoring their own manual and now has society (primarily) against them.
You have a right to "protest" on your own time, own expense and within the "bounds of lawful protest" all of which the NFL players are doing except the first. Owners can take action if they choose and fans can take action if they choose. Nobody is threatening them with their life (your Russian, China, or ISIS reference) unlike the left does at Berkeley. We just choose not to support them and don't think they should do it, which, I believe is an opinion we can hold too, right? This is not Berkeley, Hollywood or D.C. where we shut down free speech with violence, rioting and looting - and call that democratic? Only if the speech agrees with you, right?