Police need to have a valid reason to stop someone. Whether you're a driver or a pedestrian, police cannot pull you over or detain you without a viable cause of action for doing so. This cause of action could be a court-issued search or arrest warrant, or it could be a reasonable suspicion -- backed by evidence -- that you have engaged in criminal behavior.
If police perform a criminal investigation without a warrant -- or without sufficient reason to suspect you of wrongful action -- the investigation is unlawful and any resulting charges could be thrown out by a Florida court. Here are two examples of unlawful police stops: