According to the precedent, Santa Fe School District v. Doe, a teacher who allows a student to lead a prayer at a high school baseball game would most likely be ruled

In Santa Fe School District v. Doe, the Supreme Court ruled that school-sponsored prayer at public high school football games violates the Establishment Clause. A teacher leading or allowing a prayer at a school-affiliated baseball game would likewise make the prayer appear school-sponsored, so it would most likely be unconstitutional. The fact that students may practice religion does not permit school officials to promote prayer at school events.

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