WASHINGTON — In a lively and sometimes testy Supreme Court argument on Tuesday over a law banning the sale of violent video games to minors, the justices struggled to define how the First Amendment should apply to a new medium.

They tried analogies — to books, films, cartoons, comic books, fairy tales and rap lyrics. They argued about what the drafters of the Bill of Rights would have made of an extremely violent game like Postal 2.

They worried about whether it made sense to extend, for the first time, principles allowing the government to regulate depictions of sex to depictions of violence. They considered conflicting studies on the effects of violent video games on young people.

And they expressed doubt about whether the law at issue, from California, drew sensible distinctions among the games it covered.

The law would impose $1,000 fines on stores that sell violent video games to people under 18. It defined violent games as those “in which the range of options available to a player includes killing, maiming, dismembering or sexually assaulting an image of a human being” in a way that is “patently offensive,” appeals to minors’ “deviant or morbid interests” and lacks “serious literary, artistic, political or scientific value.”

“What’s a deviant violent video game?” asked Justice Antonio Scalia, who was the law’s most vocal opponent on Tuesday. “As opposed to what? A normal violent video game?” “Some of the Grimm’s fairy tales are quite grim,” he added. “Are you going to ban them, too?”

Justice Stephen G. Breyer took the other side. He said common sense should allow the government to help parents protect children from games that include depictions of “gratuitous, painful, excruciating, torturing violence upon small children and women.”

Still, most of the justices seemed to agree that a ruling in favor of the California law would require a novel extension of First Amendment principles to expressions concerning violence.

Justice Elena Kagan, the Court’s newest and youngest member, seemed to be the only justice with even a passing familiarity with the genre under review, even if it was secondhand.

“You think Mortal Kombat is prohibited by this statute?” she asked Mr. Morazzini. It is, she added, “an iconic game which I am sure half the clerks who work for us spent considerable time in their adolescence playing.”

To read more of the Court’s debate, please click here.