Wally Backman’s former girlfriend says the ex-Mets star is a drunk who came home one night and roughed her up after accusing her of sleeping with the catcher on the minor-league team he manages, according to a new lawsuit.

Amanda Byrnes, 39, said in court papers and at a press conference Tuesday that Backman went into his rage over the alleged infidelity — which she denies — after having a fight with an umpire during a Long Island Ducks game last August and getting “excessively drunk.”

“He’s a very controlling and a very sick man,” said Byrnes, who has filed a suit against the team for allowing the former Met to get hammered at the ballpark.

“He continuously put me in fear, where I had to text one of my co-workers and my mother stating that Wally is going crazy, that I’m going to need help at my house,” she said.

“Because I could see he was irrational and still hung over from the night before, which put me in fear for my safety.”

Backman, 60, was arrested after the Aug. 30 flare-up and charged with harassment and criminal mischief. Byrnes said the trouble began the day before, when Backman got into a fight with the umpires at the stadium.

“He stayed at the stadium after the game drinking,” she said. “At the Ducks’ stadium, they allow him to excessively drink.”

She said Backman later came home drunk and accused her of “having sexual involvement” with Ducks catcher Ramon Cabrera. Byrnes’ lawyer, John Ray, said she denies having a tryst with Cabrera.

But the fight continued into the next morning, with Backman — allegedly still guzzling beer at 7:20 a.m. — telling her, “you’re not going to f–king work,” Byrnes said. That’s when he threw her up against the wall, she said. Byrnes called her mother, who called cops.

Backman’s lawyer called Byrnes’ claims “nonsense.”

“Talk about fatal attraction,” attorney Stephen Civardi said. “It was too brief a relationship for him to react to it.”

He claimed Byrnes has a history of troubled relationships.

Backman, who played for the New York Mets from 1980 to 1988, has a history of criminal and legal woes himself.

The second baseman on the Mets’ 1986 world-championship team, has been making the wrong kind of headlines since he was hit with a restraining order by his first wife in 1995, claiming abuse.

In 2004 he lost a lucrative gig as manager of the Arizona Diamondbacks — just four days after being hired — when the team learned of his past.

Michael Polak, a spokesman for the Long Island Ducks, said the team does not comment on pending litigation. He said the team remained committed to Backman as its manager.