Fourth Amendment: Reasonable Suspicion

Unprovoked flight: evidence of reasonable suspicion when D runs upon noticing police in a high crime area (both alone not dispositive) (Illinois v. Wardlow)

Refusal to cooperate: no reasonable suspicion when person ignores approaching police and walks away

Anonymous tip: reasonable suspicion requires reliability in the assertion of criminal activity, and not just the identity of a person

Florida v. JL: an anonymous tip that person was at a bus stop, armed, and wearing a plaid shirt was not reliable since it does not show that the tipster had knowledge of the concealed criminal activity

Airport smuggling: little or no luggage from source city, signs of nervousness, public transportation, phone call after landing (Florida v. Royer)