West Virginia State Board of Education v. Barnette
The West Virginia Board of Education passed a resolution during World War 2 requiring that a salute to salute the flag become a “regular part of the program of activities in the public schools.”
A small group of Jehovah’s Witnesses, however, refused. They took their case to the Supreme Court.
In 1943, during the Second World War, the Supreme Court rendered its verdict.
"If there is any fixed star in our constitutional constellation, it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion, or other matters of opinion, or force citizens to confess by word or act their faith therein. "
"Nevertheless, we apply the limitations of the Constitution with no fear that freedom to be intellectually and spiritually diverse or even contrary will disintegrate the social organization. To believe that patriotism will not flourish if patriotic ceremonies are voluntary and spontaneous, instead of a compulsory routine, is to make an unflattering estimate of the appeal of our institutions to free minds. "
In other words, the power of the salute lies with the choice to salute, and the most repugnant form of censorship is compelled speech. And that is what this opposition to the NFL players protesting racial injustice represents, an unconstitutional attempt to force compelled speech or compulsory salutation.