Gigi Levangie -- the best-selling novelist who also wrote the movie "Stepmom" -- says her life is in danger ... and the alleged threat is her kid's ex-basketball coach ... this according to docs obtained by TMZ.

Levangie -- the ex-wife of Hollywood mega-producer Brian Grazer -- recently filed a request for a restraining order against Anthony Jones ... claiming he's been stalking her for several months.

In the docs, Gigi admits things weren't always so crazy with Jones ... not only did he coach her kid, she also invested in his "small business" and even allowed him to live in her guesthouse for a few weeks back in April.

But according to Gigi, something went terribly wrong -- 'cause after he moved out, Jones began following Gigi to work ... harassing her at her home and maniacally calling her on the phone -- DOZENS of times AN HOUR. Gigi claims he once trapped her in her own driveway.

Gigi says the "frightening and erratic behavior" got so bad she was forced to hire a private security team to protect her family (she and Grazer have two sons, ages 13 and 9). Gigi claims she's afraid for the safety of herself and her kids.

She is asking the court to keep Jones 100 yards away from her and her children at all times.  A hearing is set for September 12th.

We reached out to Jones for comment -- who said he had no idea about the restraining order.