Uniformed officers on patrol in an area of Chicago known for heavy narcotics trafficking saw William Wardlow standing near a building. He looked in their direction and then fled. Officers gave chase, cornered him, and detained him. A protective patdown revealed a loaded handgun illegally carried, and Wardlow was arrested.
The Illinois Appellate Court and Illinois Supreme Court ruled that Wardlow was unlawfully detained without reasonable suspicion, and ordered the gun suppressed. The U.S. Supreme Court reversed. Although agreeing that a person's mere presence in a high-crime area is not enough by itself to justify detention, the court said that when coupled with sudden flight, adequate justification exists.
In the court's words, "It was not merely defendant's presence in an area of heavy narcotics trafficking that aroused the officer's suspicion, but his unprovoked flight upon noticing the police. Evasive behavior is a pertinent factor in determining reasonable suspicion. Headlong flight is the consummate act of evasion. We conclude that the officer was justified in suspecting that Wardlow was involved in criminal activity, and, therefore, in investigating further."
In practice, officers intending to rely on Wardlow to validate detentions of suspects who flee and are pursued and caught should be prepared to explain why they consider an area a "high-crime" location. For example, departmental statistics on the number of drug or other arrests made at a location, or within a particular radius and within a specified period of time before the incident, might be sufficient. It would generally not be enough to simply make the unsupported claim that a certain place was a high-crime area.
If you go in foot pursuit of a suspect who runs on your approach in a high-crime area, you should yell, "Stop! Police!" as you chase him. This will constitute an attempt to make a lawful detention. A suspect who continues fleeing would then be in violation of any applicable statutes making it a crime to resist, delay, obstruct, or interfere with a police officer in the lawful performance of official duties, and provide a ground for arrest (and therefore a full search incident to arrest).