Definition - What does Reasonable Belief mean?
Reasonable belief is when a law enforcement officer has a definite reason to believe that a crime or criminal behavior is currently taking place. If a law enforcement officer has valid reasonable belief, then they do not need a warrant to make a search or seizure, nor to make an arrest.
Justipedia explains Reasonable Belief
If a law enforcement officer does not have reasonable belief, then they are required to have a warrant to make searches and seizures.
A situation that may cause reasonable belief is if a police officer witnesses a bank robbery occur, and they pursue the bank robber(s) in their cruiser. If the officer caught up to them, they could apprehend them, arrest them, and make searches and seizures of their property. This is because witnessing the robbery provided the police officer with the requisite reasonable belief.