Hawzah News Agency – Joseph Kennedy, who used to be an assistant coach for a high school football team near Seattle, pointed to the spot on the 50-yard line where he would take a knee and offer prayers after games.

He was wearing a Bremerton Knights jacket and squinting in the drizzling morning rain, and he repeated a promise he had made to God when he became a coach.

“I will give you the glory after every game, win or lose,” he said, adding that the setting mattered: “It just made sense to do it on the field of battle.”

Coaching was his calling, he said. But after the school board in Bremerton, Wash., told him to stop mixing football and faith on the field, he left the job and sued, with lower courts rejecting his argument that the board had violated his First Amendment rights.

The Supreme Court will hear arguments in the case on Monday, and there is good reason to think that its newly expanded conservative majority will not only rule in Mr. Kennedy’s favor but also make a major statement about the role religion may play in public life. The court’s decision, expected by June, could revise earlier understandings about when prayer is permitted in public schools, the rights of government employees and what counts as pressuring students to participate in religious activities.

The two sides offer starkly different accounts of what happened and what is at stake. To hear Mr. Kennedy tell it, he sought only to offer a brief, silent and solitary prayer little different from saying grace before a meal in the school cafeteria. From the school board’s perspective, the public nature of his prayers and his stature as a leader and role model meant that students felt forced to participate, whatever their religion and whether they wanted to or not.

The community in Bremerton appeared to be largely sympathetic to Mr. Kennedy, who is gregarious, playful and popular. But the school board’s Supreme Court brief suggested that some residents opposed to prayer on the football field may have hesitated to speak out given the strong feelings the issue has produced.

“District administrators received threats and hate mail,” the brief said. “Strangers confronted and screamed obscenities at the head coach, who feared for his safety.”

Rachel Laser, the president of Americans United for Separation of Church and State, which represents the school board, said, “What we’re focused on is the religious freedom of students.”

“Going to the 50-yard line directly after the game when you’re the coach, with the students assuming they’re supposed to gather with the coach, and praying at that time puts pressure on kids to join,” she said.

Mr. Kennedy acknowledged that, as time went on, students did join him.

“I started out praying by myself,” he said. “I guarantee it was no longer than 10 seconds.”

When athletes asked to participate, he said he told them that America was a free country.

“It was,” he added, “never any kind of thing where it was a mandatory thing.”

Asked whether some athletes might have felt compelled to join in, he gave a stock response. “I coached for about eight years and there were about 60 kids on the team each year,” he said. “I challenged every news reporter and said: ‘Find somebody.’”

Even residents of Bremerton who disagreed with Mr. Kennedy about his prayers said he was deeply engaged in his duties, serving as a surrogate father to many troubled teenagers.

“I have nothing but respect for Coach Kennedy,” said Paul Peterson, who worked with Mr. Kennedy for years at the Puget Sound Naval Shipyard. “There have been countless young men who have stood up and said what a great influence Coach Kennedy was. But on this specific thing — and I’ve told this to Joe — I feel he’s misdirected.”

Asked about Mr. Kennedy’s challenge to find a student who had been coerced into praying, Mr. Peterson said it was not the first time he had heard the question.

“He said the same thing to me,” Mr. Peterson said. “I said it may not have been explicit coercion, but there was an implicit coercion. When the coach goes out to the 50-yard line, he has something to say.”

Over the last 60 years, the Supreme Court has rejected prayer in public schools, at least when it was officially required or part of a formal ceremony like a high school graduation. As recently as 2000, the court ruled that organized prayers led by students at high school football games violated the First Amendment’s prohibition of government establishment of religion.

“The delivery of a pregame prayer has the improper effect of coercing those present to participate in an act of religious worship,” Justice John Paul Stevens wrote for the majority.

Mr. Kennedy’s lawyers said those school prayer precedents were not relevant because they involved government speech. Rather, they said, the core question in Mr. Kennedy’s case is whether government employees give up their rights to free speech and the free exercise of religion at the workplace.

The school district, its lawyers responded, was entitled to require Mr. Kennedy to stop praying as he had. “Regardless of whether Kennedy’s very public speech was official, the district could regulate it,” the school district’s Supreme Court brief said. “His prayer practice wrested control from the district over the district’s own events, interfered with students’ religious freedom and subjected the district to substantial litigation risks.”

The sweep of the Supreme Court’s decision may turn on which side’s characterization of the facts it accepts. But even a modest ruling in Mr. Kennedy’s favor, saying that his private, solitary prayer was protected even if it took place in public and at least tacitly invited students to participate, would represent a sea change in the court’s approach to the role religion may play in public schools.

Mr. Kennedy was born in Bremerton, which is just across the Puget Sound from Seattle but in some ways worlds away. “Friday nights at the Bremerton High School football field were small-town Americana kind of events,” Mr. Peterson said.

Mr. Kennedy’s early years were troubled, he said, but he straightened out in the Marine Corps, serving for two decades. Returning home in 2006, he went to work at the shipyard. Not long after, he was offered a spot as an assistant coach, a big commitment that came with a modest stipend of about $4,500 for the season.

As he weighed the offer, he happened upon a football movie on television, “Facing the Giants.”

“God came down and just gut-punched me and answered the question of whether I should coach,” Mr. Kennedy said. The answer: “Absolutely.”

The idea of thanking God after games came from the movie, he said: “I kind of plagiarized it.”

Mr. Kennedy said he prayed after games for years without controversy. If parents asked what he was doing, he said he was “just thanking God.” If they said they did not want their children to take part, he told them that was fine.

He also led students in prayer in the locker room, a practice neither he nor his lawyers now defend.

The sole issue in the case, said Hiram Sasser, a lawyer with First Liberty Institute, which represents Mr. Kennedy, was whether he could offer a silent, solitary prayer on the field after the game.

“If somebody comes near you,” Mr. Sasser added, “you don’t need to run away.”

The school district countered that the context mattered, noting that a judge on the U.S. Court of Appeals for the Ninth Circuit, in San Francisco, had criticized what he called “a deceitful narrative” created by Mr. Kennedy’s lawyers.

Mr. Kennedy was never disciplined for offering silent, private prayers, the judge, Milan D. Smith Jr., wrote last year. Instead, the judge wrote of one game, Mr. Kennedy “prayed out loud in the middle of the football field” just after it finished, “surrounded by players, members of the opposing team, parents, a local politician and members of the news media with television cameras recording the event, all of whom had been advised of Kennedy’s intended actions through the local news and social media.”

Things came to a head in 2015, after an opposing coach told Bremerton High School’s principal that he thought it was “pretty cool” that Mr. Kennedy was allowed to pray on the field. The school board told Mr. Kennedy that he could pray if it did not interfere with his duties and did not involve students.

He said he complied. But tensions continued to rise, and the dispute became increasingly public.

At a game that October, Mr. Kennedy said his prayer while surrounded by coaches and players from the opposing team, members of the public and a state lawmaker. A photograph shows a substantial group kneeling with the coach.

After two more games that month at which Mr. Kennedy continued to pray, the school board put him on paid administrative leave.

A school official recommended against renewing the coach’s contract for the 2016 season, and Mr. Kennedy did not reapply for the position.

When the Supreme Court refused to hear an earlier appeal in the case in 2019, four justices expressed qualms about how Mr. Kennedy had been treated.

“The Ninth Circuit’s understanding of the free speech rights of public-school teachers is troubling and may justify review in the future,” Justice Samuel A. Alito Jr. wrote at the time, adding that the justices should wait for more information about “important unresolved factual questions.” He was joined by Justices Neil M. Gorsuch, Brett M. Kavanaugh and Clarence Thomas.

After further proceedings, the Ninth Circuit again ruled for the school board. This time, the Supreme Court agreed to hear the case.

Lawyers for the school board acknowledged that they faced headwinds at the Supreme Court.

“We know that this is a tough hill to climb,” Ms. Laser said, adding that a decision in Mr. Kennedy’s favor in the case, Kennedy v. Bremerton School District, No. 21-418, “would give a license to coaches and teachers across the nation to engage in coercive prayer.”

Mr. Kennedy has moved to Florida to help his wife care for her ailing father. If the Supreme Court rules in his favor, he said, he will be on “the very first flight back.”

“The biggest honor of my life was coaching these young men,” he said. “No lie, we had blood, sweat, tears and death in the Marine Corps, but I got way more out of coaching than anything else in my life.”