In 1986, Tyrone Foster, an African American, killed Queen Madge White, a white 79-year-old, as part of a burglary in Rome, Georgia. He was arrested and quickly confessed. His lawyers argued that his limited mental ability meant he could not form the requisite intent to commit capital murder, meaning that he could not be sentenced to death. An all-white jury, however, disagreed.

Before the Supreme Court, Foster argues that the jury was unfairly stacked against him because the prosecution used “peremptories” to remove all African American jurors from the panel. His counsel at the time raised an objection under Batson; but the prosecution gave “race-neutral” explanations. It said, for example, that one black juror was “a social worker”—she wasn’t. The judge accepted them. In his closing argument, the prosecutor asked the jury to vote for death in order to “deter other people out there in the projects from doing the same again.”

Nearly two decades later, Foster’s lawyers obtained the prosecution’s notes for jury selection. The state’s lawyers had marked each black juror’s name with a “B,” and a state investigator had specifically ranked each “B” juror in order of preference if “it comes down to having to pick one of the black jurors.”

Lawyers can block potential jurors in one of two ways. The first is “for cause,” meaning, for example, that a juror is related to a witness or a party, or has some other genuine conflict of interest. The other is the “strike,” which means only that there’s something—maybe even something not clear—about that juror the lawyer just doesn’t like.

Peremptory strikes have been part of common-law trials since at least the Assize of Clarendon in 1166. They have stirred unease almost as long; in 1305, the English Parliament banned the Crown from using them. Common-law judges, however, immediately reinvented the “strike” as a motion to “stand aside” a juror, and they persisted another half-millennium, until they were finally abolished in England by the Criminal Justice Act of 1988.

In the U.S., they live on in both federal and state systems. The prosecution and defense alike use them to game the jury, picking jurors they think will be favorable to their cause. The challenges may be based on a hunch; but they may also be based on demographics factors like age, education, income, neighborhood—and race, an overwhelming fact of American society. Ignoring these factors would be bad lawyering.

Batson, however, tried to put race off-limits as a motivating factor. Race-based peremptories, the Court said, violate the equal-protection rights both of the defendant and of the potential juror.

So was created the “Batson hearing.” When one party notices the other making a suspicious series of challenges, he or she can ask the court to order the other party to explain themselves. The other party then must give “race-neutral” reasons why the juror didn’t suit. If those explanations are accepted, the trial goes on; if the court finds “purposeful discrimination,” however, then the court must order a remedy, usually a halt in the trial until a new jury panel can be assembled. If a trial court rejects a Batson motion, an appellate court may reverse that decision—but only if the judge’s ruling was “clear error.” If that happens, the defendant gets a new trial.