Montague was expelled in February after the decision by a sexual misconduct panel that investigated his 2014 encounter with a woman who is now a junior at Yale.
The lawsuit asked that Montague be reinstated, alleging that Yale made him a scapegoat amid criticism the university was soft on male students accused of sexual assault.
"Mr. Montague -- captain of Yale's basketball team and one of the most prominent male students on campus -- was Yale's ticket to restoring its tarnished image," said a statement from a public relations firm representing him.
In a statement Thursday, university spokesperson Thomas Conroy said the lawsuit is "factually inaccurate and legally baseless, and Yale will offer a vigorous defense."
The Yale panel is similar to those used at other schools to investigate claims of sexual assault on campus. The investigative procedures are guided by the Department of Education's recommendations of how schools ensure compliance with Title IX federal law.
"Unfortunately for Montague, he was a prime candidate to serve as Yale's poster boy for tough enforcement of its Sexual Misconduct Policies: popular, well-liked and respected amongst his peers at Yale, and known throughout the country as one of Yale's most promising men's basketball stars," the lawsuit said. "In short, imposing harsh discipline on Montague would surely make an impact."
The suit said Montague had never been the subject of a sexual assault complaint but his accuser was told by those investigating her allegations that he had assaulted another student. The earlier incident involved an accusation that the ex-player had rolled up a paper plate and shoved it down the shirt of a female student.
"The actions taken by the defendants resulted from a deeply flawed process during which the plaintiff was denied the most rudimentary elements of fairness promised to him by Yale," the suit said.
The night in question
Montague's lawyers have said the former team captain and the female student developed a relationship that led to their sleeping together in his room four times in fall 2014.
What is in dispute is the fourth occasion. According to a statement from Montague attorney Max Stern, the two had consensual sex and then went separate ways. The statement said that later that night, she reached out to him to meet up, returned to his room voluntarily and spent the night in his bed with him. However, the woman stated she did not consent to sexual intercourse, while Montague said she did, the statement said.
"A year after the fact, the female student -- who was affirmatively misled by the defendants into participating in a formal complaint process initiated by Yale and not by the student herself -- claimed that just part of her encounter with Montague (the intercourse) was nonconsensual," the lawsuit said.
"And she made this claim despite calling Montague shortly after the encounter, voluntarily rejoining him the same evening, flirting with him on the way back to his bedroom, and spending the remainder of the night in his bed with him."
What schools are supposed to do
The panel that recommended expelling Montague is the University-Wide Committee on Sexual Misconduct
, which was instituted in 2011. That was around the time the federal government investigated the university for alleged Title IX violations involving the way it handled reports of sexual misconduct.
Title IX bars gender discrimination in education. The Department of Education interprets Title IX to say that sexual harassment is a form of sex discrimination, and therefore schools could be held responsible if they don't investigate and adjudicate these cases. It requires schools to "respond promptly and effectively" to allegations of sexual harassment or violence.
In a letter sent to universities and colleges in April 2011, the Office of Civil Rights division of the Department of Education discussed the obligations schools have to investigate claims and listed the following guidelines:
-- Disseminate a notice of nondiscrimination.
-- Designate at least one employee to coordinate its efforts to comply with and carry out its responsibilities under Title IX and
-- Adopt and publish grievance procedures for complaints.
According to the OCR, those procedures must allow both sides to make their case, possibly by presenting witnesses and evidence. Committees must make a decision based on a 'preponderance of evidence,' which is a legal term based off the believability of evidence rather than the amount. Finally, once decisions are made, the OCR requires school committees to notify both parties of the committee's decision.
However, the procedures schools adopt to follow these federal guidelines differ from campus to campus and from case to case.
And in some cases, they are called into question. The DOE's Office for Civil Rights is looking into 219 cases at 173 colleges and universities. Open investigations look into the fairness of the school's adjudication proceedings.
Yale University is not on that list.
How Yale handles sex misconduct cases
The University-Wide Committee at Yale oversees formal complaints of sexual misconduct. Conroy has said each case before the committee adheres to a specific process.
Impartial "fact finders," who are usually lawyers, investigate the claims and report their findings to the five-person panel. The panel then meets with both parties, who each tell their version of what happened and answer questions. The panel then determines by majority vote whether Yale's sexual misconduct policy was violated.
A recommendation is then made as to what disciplinary action, if any, should be taken.
Conroy has defended the university's system.
"The UWC's procedures have been revised every year to take into account lessons learned over the preceding year," he says.