This is a great case out of Fairfield County.  Basically, a police officer stopped a car because he heard the Defendant rev his engine and it appeared as though he was traveling faster than the posted speed limit.  Thankfully, the Court of Appeals held that the police officer did not have probable cause to stop the car and threw the case out.

Below is a case out of Columbus, Ohio where a person was stopped for just having a license plate light burnt out.  Make sure your license plate light is working, if not you could end up with a DUI.

Simply put, the Courts fill in the blanks.  Legislature passes a law and then as cases are decided and appealed the blanks are filled in.  Easy example:  Ohio legislature passes a law stating you can't drive a vehicle under the influence.  Sounds simple enough right?  Not so simple.  What exactly is a vehicle?  A car?  Of course...what about a Segway?  Hmm.  That's where the court's come into play.  Let's say Jimmy is arrested for a DUI on his Segway and a Jury finds him guilty.  Well, Jimmy can appeal that conviction to the court of appeals.   The court of appeals will then decide if a Segway is a vehicle.  If they decide that it isn't, then going forward you can't be charged with a DUI on your Segway.  The decision is only binding on the area which the that court of appeals controls.  This is a simplified explanation so do some reading if you want to know more.

This case pretty much gives police officers the ability to stop anyone for any violation of the law.  http://en.wikipedia.org/wiki/Whren_v._United_States

If you want to learn more about probable cause you have to start with Terry v. Ohio.  Read the cliff notes version at wikipedia:  http://en.wikipedia.org/wiki/Terry_v._Ohio