The 180degrees Rule

The 180degree rule is a basic rule in cinematography... it is put in place so the viewer doesn't get their perspective all wrong.

Film makers draw an imaginary line across the scene where they can't cross. They can do whatever they like within the boundary, but as soon as they cut to the other side of the line viewers get confused as continuity is ruined with the characters seemingly looking at different place.

This rule is followed no matter the scene, whether simple dialogue or a full action fighting scene, the rule is always followed.

There is one exception however, if the camera arcs behind the line in one movement it can be accepted as the viewers see the change in angle. As long as they keep within the new line with the camera, it should all be good.

My own example