The documentary “RBG” gave an entertaining and well-rounded look at the life and career of Supreme Court Justice Ruth Bader Ginsburg. She’s the judicial equivalent of a pop star, and there’s enough fascinating fodder on the record to make an equally strong dramatic film about her.

Too bad that this isn’t the one. It’s written by first-time scripter Daniel Stiepleman, who imbues it with predictable dialogue, and directed by journeywoman filmmaker Mimi Leder, whose résumé includes the awful thriller “The Peacemaker,” the by-the-numbers sci-fier “Deep Impact,” and the schmaltzy drama “Pay It Forward.”

But the film’s main problems reside elsewhere. The first one has to do with the preview trailer, the one that’s being blasted all over broadcast television, the one that suggests the film is about something that it’s not about.

“Women are too emotional to be lawyers” is mentioned in it. There’s also the line, “If the law differentiates on the basis of sex, then how will women and men ever become equal?” Or how about “You will lose (this case) and when you do you will set the women’s movement back 10 years.”

Ah, but buried in the middle of the misleading ad is the quickly uttered sentence, “This is sex-based discrimination against a man.”

That last part, likely to the chagrin of so many potential viewers who believe this is a film focused on women’s rights, is what the film is about. It’s not a biography of Ginsburg, it’s a dramatized look at her days as a struggling law student, a frustrated job seeker, the relationships with her husband Martin and her teenage daughter Jane, and it eventually centers on a case that got her noticed.

But that case is about taxes and sex discrimination and, as is practically hidden in that trailer, involves the rights of a man not a woman. Worse, it’s a confusing and ultimately uninteresting case.

The film starts promisingly, showing hordes of men in dark suits, and one woman in a bright blue outfit, climbing the steps of Harvard Law School in 1956, just six years after the institution decided to accept women into its fold. And there’s Ruth Ginsburg (Felicity Jones) in the lecture hall, listening to a thoughtlessly sexist dean (Sam Waterston) address all of the “Harvard men.” Ginsburg keeps being ignored in classes, but is never afraid to speak up, to prove that she can hold her own, maybe even gain some respect. Martin (Armie Hammer), a year ahead of her in law school, develops some medical issues, and she, showing ambition and tirelessness, takes on a double load by sitting in on his classes for him.

But a few years later, he lands a tax law job while she, facing the discriminatory reality of being “a woman, a mother, and a Jew,” can only get a teaching gig, specializing, however, in “Sex Discrimination and the Law” at Rutgers.

Another decade elapses before the film gets to its point: A case taken by both Marty and Ruth involving Charles Moritz (Chris Mulkey), a man trying to be a caregiver for his ailing mom, but needing to hire a nurse, then writing off those expenses and being told that’s illegal, that only women can be caregivers and can take deductions.

That’s it. That’s the whole movie, focusing on this rather uninteresting case, the details of which become as difficult to follow as the discussion on shorting stocks near the end of “Trading Places.” A few noteworthy characters make appearances, including the fiery women’s right lawyer Dorothy Kenyon (Kathy Bates) and the excitable ACLU lawyer Mel Wulf (Justin Theroux), but there’s not a lot of depth offered by anyone else. Jones gives Ginsburg a few touches of pizzazz and shows a good amount of emotion through her eyes, and Hammer plays it in a nonchalantly likeable manner, but their - and others’ - performances are relatively flat.

The cliché playbook is pulled out for the film’s big courtroom scene, in which one of the judges suggests that a woman in the kitchen is the natural order of things, then a follow-up has Ginsburg going full-blown Hollywood with a passionate, hit-you-over-the-head big message speech.

But it’s a vanilla movie, ending, not very imaginatively, with Ginsburg climbing another long flight of steps, this time in D.C.

Ed Symkus writes about movies for More Content Now. He can be reached at esymkus@rcn.com.

“On the Basis of Sex”

Written by Daniel Stiepleman; directed by Mimi Leder

With Felicity Jones, Armie Hammer, Justin Theroux, Chris Mulkey

Rated PG-13