The Bremerton High School athletic director seemed sure that my experience training Marines to work as a team was all the qualification I needed to be a football coach. As I weighed the opportunity, I caught the movie “Facing the Giants.” It seemed an answer from God. I committed to coaching football and promised God that I would take a knee by myself in quiet prayer at the 50-yard line following every game, win or lose.

Over the years, my prayers developed into motivational talks in which I led players who chose to join me in prayer. When the school district eventually told me to stop doing that, I did. My commitment with God didn’t involve others. It was only to pray by myself at the 50-yard line after each game.

But then the school district got lawyers involved, and they kept shifting the goal posts every time I complied. Eventually they said I had to refrain from any “demonstrative religious activity” visible to students or the public. They suggested instead I walk across the field, up the stairs, across a practice field, into the main school building, down the hall and into the janitor’s office if I wanted to pray after games.

I thought that would send a message that prayer is something bad that has to be hidden. I couldn’t send that message. So I simply asked to continue praying quietly on one knee at the 50-yard line after each game.

Two days after my last postgame prayer, the school suspended me, even though it acknowledged there was “no evidence that students have been directly coerced to pray with” me, and that I had complied with its directives “not to intentionally involve students.” The school then gave me the first negative evaluation in my file, adding: “Do Not Rehire.” I was fired for taking a knee in prayer by myself at the 50-yard line for 15 to 30 seconds after high-school football games.

Unless the U.S. Supreme Court rules in my favor, teachers could be fired for praying over their lunch in the cafeteria if students can see them. That doesn’t seem like the Constitution I fought for in the Marine Corps.

I just want to be back on the field with my guys, building a team to accomplish a mission. I hope the Supreme Court agrees.

Mr. Kennedy is a Marine Corps veteran and the appellant in Kennedy v. Bremerton School District, on which the Supreme Court will hear oral arguments Monday.