Joe Kennedy, a Washington state high school assistant football coach who won his Supreme Court battle last year after fighting for his right to pray on the gridiron, said Wednesday he has resigned from his position after only one game. 

In a statement obtained by Fox News Digital from the First Liberty Institute that included Kennedy's resignation letter, he claims that the Bremerton School District retaliated against him after he was reinstated. 

Kennedy said other reasons factored into his decision to step down from his assistant football coaching position at Bremerton High School, including that he needed to care for an ailing family member out of state. He had been living full-time in Florida, and before the first game last Friday he said he didn't know if he'd continue coaching.

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"[I]t is apparent that the reinstatement ordered by the Supreme Court will not be fully followed after a series of actions meant to diminish my role and single me out in what I can only believe is retaliation by the school district," Kennedy wrote. 

"Therefore, I am tendering my immediate resignation." 

Photo of Former Bremerton High School assistant football coach Joe Kennedy

Former Bremerton High School assistant football coach Joe Kennedy answers questions after his legal case, Kennedy vs. Bremerton School District, was argued before the Supreme Court, April 25, 2022, in Washington, D.C. (Win McNamee/Getty Images/File)

"I believe I can best continue to advocate for constitutional freedom and religious liberty by working from outside the school system so that is what I will do," Kennedy wrote. "I will continue to work to help people understand and embrace the historic ruling at the heart of our case."

Kennedy lost his job in 2015 and waged a seven-year legal battle to get it back. School district officials had asked him to keep any on-field praying non-demonstrative or apart from students, saying they were concerned that tolerating his public post-game prayers would suggest government endorsement of religion, in violation of the separation of church and state.

Football coach Joe Kennedy walks near the Supreme Court

Former Bremerton High School assistant football coach Joe Kennedy holds hands with his wife Denise as he walks in front of the U.S. Supreme Court with members of his legal team after his case, Kennedy vs. Bremerton School District, was argued before the Supreme Court, April 25, 2022, in Washington, DC. (Win McNamee/Getty Images/File)

He insisted on praying publicly at midfield after games, and the district placed him on leave and declined to renew his contract.

Last year, the U.S. Supreme Court's conservative majority sided with him, with Justice Neil Gorsuch writing that "the best of our traditions counsel mutual respect and tolerance, not censorship and suppression, for religious and nonreligious views alike."

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Hiram Sasser, executive general counsel at First Liberty Institute, which represented Kennedy during his legal battle, said the organization would investigate Kennedy’s claims of retaliation. 

"We have come to learn of serious allegations of retaliation against coach Kennedy by the Bremerton School District," Sasser said.

"They’ve done everything they can to make him feel unwelcome. We are going to investigate the situation to determine whether further legal action is necessary." 

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Bremerton School District said it had received Kennedy's resignation and it is pending approval at a meeting scheduled for Thursday. 

The district did not comment on Kennedy's allegations of retaliation. 

The Associated Press contributed to this report.