Our flag stands for individual liberty and freedom of conscience, not lockstep uniformity and coercion. Traditionally, players have stood during the anthem to show respect for the flag. But if to force a show of respect for a symbol of freedom, it comes to the use of coercion and punishment, we are dishonoring that symbol, and the freedom it represents, far worse than they could ever do.
A patriotic display is voluntary. In places where it isn't voluntary, it's a meaningless and empty gesture in capitulation to tyranny.