In the case of Illinois v. William aka Sam Wardlow, 1999, the U.S. Supreme Court ruled that police officers can stop and search individuals without a warrant if they flee at the sight of law enforcement in an area known for heavy crime. The case began when Chicago police saw Wardlow run after spotting their patrol car in a high-crime neighborhood. After catching him, they conducted a protective pat-down search and found a .38-caliber handgun which led to his arrest on unlawful use of weapon charges. In court, Wardlow argued that he was unlawfully stopped because running from police does not constitute reasonable suspicion for a stop-and-frisk under the Fourth Amendment's protection against unreasonable searches and seizures. However, by an 8-1 majority decision (Justice Stevens dissenting), it was held that unprovoked flight upon noticing the police is certainly suspicious behavior justifying further investigation.

In the dissenting opinion for Illinois v. Wardlow, Justice Stevens argued that an individual's presence in a high-crime area and unprovoked flight upon seeing police officers does not necessarily indicate criminal activity. He contended that there are many reasons why someone might run when they see the police, even if they have done nothing wrong - fear of racial profiling or harassment by law enforcement being among them. Therefore, he believed it was unjust to assume guilt based on such behavior alone. Furthermore, Justice Stevens expressed concern about the potential for abuse of power by law enforcement officials who could use this ruling as justification for stopping anyone who runs from them without any other evidence of wrongdoing.