The case you’re talking about is Illinois v. Wardlow.
Here’s the way this works. When the police stop you, they are sometimes permitted to frisk you for their own protection, even without probable cause. What they must have is a “reasonable, articulable suspicion,” that a crime is being being committed or is about to be committed. This was decided by a case called Terry v. Ohio, (392 U.S. 1, 1968.)
Please note that the police don’t have to have any suspicion to come up to you and ask you questions. As long as you’re free to ignore them and walk away, it is a completely consentual encounter that doesn’t implicate the Constitution at all. But if they have that reasonable, articulable suspicion, they can briefly detain you and pat down your outer clothing, just to make sure you don’t have a weapon that might threaten their safety.
This is not a full-scale search. It’s just a brief check. The law allows this, explained the Terry Court, under the theory that the compelling society interest is so great (protection of police officers’ lives) and the intrusion into individual privacy so small (just a brief pat of outer clothing) that, on balance, it’s considered appropriate.
I can’t imagine that anyone would argue that those rules are unfair, or involve undue police powers.
Since 1968 and the Terry decision, plenty of cases have attempted to create a bright-line test for what, exactly, constitutes “reasonable, articulable suspicion.” It’s never really been done, but one phrase appears in hundreds of appellate opinions: “totality of the circumstances.” The general consensus is that in deciding whether reasonable suspicion exists is done by taking into account all the circumstancesm rather than focusing myopically on the presence or absence of one element.
An individual’s presence in a high-crime area, standing alone, is insufficient to create reasonable suspicion. But it can add to other factors. Nervous or evasive behavior when encountering police, standing alone, is not sufficient. But the two together (and as the Wardlow Court dryly observes, “…headlong flight is the consummate act of evasion”) may serve to create a reasonable suspicion under Terry.
So, the officers pursued Wardlow, made a Terry-type stop, and frisked his outer clothing only. They discovered a concealed handgun, a violation of Illinois law. At that point, they arrested Wardlow, and he was ultimately convicted of possession of a handgun by a felon.
Frankly, there is very little landmark or new about this case; it is governed by the principles of a case decided in 1968, which has been good law for 31+ years.
And I don’t think it gives the police undue powers.