Sam Setzer filed for a restraining order against Rosa, and in the docs he says she's been terrorizing him ever since their March 19 breakup. Sam says Rosa -- who played murdered nurse Maria on season 1 of 'AHS' -- showed up at his house around midnight, rang his doorbell and screamed loudly enough to wake his neighbors. He's pretty confident she was intoxicated.

In the docs, obtained by TMZ, he says Rosa threatened to call cops and lie about him hitting her. Sam says he decided to call cops first, and that's when Rosa bolted. Besides that horror show, he says Rosa's flooded him with calls and texts ... including one that said, "If pushed I can be a stressful/stressed person." Mind you, Sam says they only dated for a month.

He was granted the restraining order which requires her to stay 100 yards away from him.

Ya might also recognize Rosa from the "Parenthood" TV series. She was far less scary on that than 'AHS' ... though Sam probably doesn't think so. She's also slated to star in the Robert Rodriguez/James Cameron blockbuster, "Alita: Battle Angel" ... coming out in December.