ON SEPTEMBER 29th, at 7pm, when the Parkway Panthers face the Airline Vikings in a high-school football clash in Bossier City, Louisiana, the drama will begin before the first snap. The previous day, the principal of Parkway High School sent a letter to student athletes warning them not to mimic the widespread protests that took place over the weekend at National Football League (NFL) games. Parkway players attending “any sporting event in which their team is participating”, wrote Waylon Bates, the principal, must “stand in a respectful way throughout the National Anthem”. Anyone who kneels, sits or makes any sign of disrespect will risk being benched, or, with “continued failure to comply”, subjected to “removal from the team”.

With its legalistic language, this pre-emptive strike against student protestors is different in tone to President Donald Trump’s jeering call for NFL team owners on September 23rd to fire any “son of a bitch” who “disrespects our flag”. But the demand, like Mr Trump’s call, brooks no dissent. Principal Bates says his school is “committed to creating a positive environment for sporting events” and will crack down on any students who cause a “disruption” to the game.

Some critics of Mr Trump say his tirade and follow-up messages on Twitter violated the First Amendment. It’s true that his words chafed against the spirit of free expression, but it is a stretch to say that the president's appeal to NFL owners violated the constitution. A “state-action” requirement applies to constitutional rights: if your neighbour or your boss or your parent tries to silence you, you generally have no justiciable constitutional claim. But if an arm of the government—Congress, a state legislature, a town council, a city agency, the public transportation authority—interferes with your right to speak, you just might have a case. As a Louisiana public school, Parkway High is an arm of the state, and Principal Bates is an agent thereof. He is subject to the constraints of the First Amendment.

What do the courts say about the free-speech rights of schoolchildren? Administrators and teachers have wide latitude in day-to-day matters. They can shush unruly students, punish children who use crude or obscene language and hold students accountable when they submit plagiarised essays, cheat or lie. But when it comes to the expression of opinions and beliefs—particularly political and religious ideas—schools must grant children a wide berth. Two landmark Supreme Court cases vindicate youngsters’ rights, and they quite clearly protect any Parkway football player who may prefer not to follow his principal’s respect-the-anthem directive tonight.

The first case, decided in 1943, upheld the right of Jehovah’s Witnesses to opt out of a daily flag salute ceremony at school. The students’ request was based on their reading of a line in the Book of Exodus that prohibits paying homage to a graven image, but in West Virginia v Barnette, the Supreme Court painted the matter in far broader terms. Barnette powerfully explains why mandated professions of belief clash with the First Amendment. “If there is any fixed star in our constitutional constellation”, Justice Robert Jackson wrote, “it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion or other matters of opinion”. Nor can the government “force citizens to confess by word or act their faith therein”.

Requiring students to stand respectfully during the singing of the national anthem is to “prescribe what shall be orthodox” during Parkway High football games. It forces young citizens to affirm a particular patriotic message. Officials, whether high or petty, cannot do that. And in 1969, a 7-2 majority in Tinker v Des Moines School Board clarified the rule. The Supreme Court stood up for the rights of middle-school and high-school students who had been suspended for wearing black armbands to school, an expression of their opposition to America's involvement in the Vietnam War. Justice Abe Fortas wrote that a classroom should be a “marketplace of ideas” and that neither students nor teachers “shed their constitutional rights to freedom of speech or expression at the schoolhouse gate”.

The Tinker court sweepingly rejected the schools’ contention that banning armbands was necessary to avert a pedagogical debacle. The students’ expression is “akin to ‘pure speech’”, Justice Fortas wrote. “It does not concern aggressive, disruptive action or even group demonstrations”. An administrator’s general “fear or apprehension of disturbance is not enough to overcome the right to freedom of expression”. This nearly half-century-old lesson is a startlingly appropriate rebuke to Principal Bates (who asserts without elaboration that any dissent would entail "disruption"), and is even more persuasive applied to the setting of a football field rather than a classroom. There is no reason to think that a few students taking a knee or linking arms could spur a breakdown of civic order under the lights on a field in Louisiana. And Justice Fortas reminds us that even if there is some chance of raucous protests swelling after players defy their principal to call attention to police brutality, racial injustice—and, now, presidential disdain for free expression—“our constitution says we must take this risk”.