The 4th Amendment of the United States Constitution protects citizens from unreasonable searches and seizures. If police contact with a citizen rises to the level of a "seizure," it must be supported by some level of suspicion that the citizen is or has been engaged in an unlawful activity. The main question in determining whether a seizure has occurred is. "would a reasonable person feel free to leave the encounter with the officer." To answer this question, courts look to the totality of the circumstances surrounding the police/citizen encounter.
The specific facts the courts look for are: did the police officer use any show of authority during the encounter; what was the police officer's demeanor; did the police officer restrain the citizen's movement or freedom either through use of restraints or commands.
After analyzing the specific police encounter, the court makes a determination as to whether a seizure has occurred for constitutional purposes.