The right to peaceful protest covers everyone including players. As far as I know, there are no conditions (players can't do it, can't do it during the anthem, can't do it at work, etc.) to exercising those rights nor should there. If it's not right for players to protest while at work, then by extension it's not okay for ordinary workers to protest at work about issues like safety, hours of work, pay, etc. These two groups have have vastly different agendas, but they are still exercising their rights.
You should also know that employees have the many rights like filing a grievance (protest) and cannot be punished by their employer. Employees must have a certain amount of hours off from work, meal times, paid time off, public holidays off, etc. Employees have those rights because people in the past fought long and hard and protested to get them.
The reason to protest is to bring light to issues that the half-asleep masses don't know or care enough about. That's why you protest in public and not in the basement. If you want to make a statement, the best place to do it would be during a game watched by millions of people. Make no mistake that the players protested peacefully during the anthem. They were not rioting in the streets, damaging windows, burning police cars, or stopped the game to protest. The inconvenience to you (if you can even call it an inconvenience) is very minor. You give Steven Seagal way too much credit if you compare a minor inconvenience like this to being held hostage.
That being said, I think people should be careful where they choose to protest. It was irresponsible for the Tamils to block the Gardiner Expressway because people could have caused serious accidents.
It is far more disrespectful to the flag that we complain about people exercising their rights when we enjoy those same rights. If you don't think that's the case, then visit a place like Tianamen Square in Beijing, China where waving the wrong flag gets you thrown in jail without a trial.