the 180 Degree rule

The 180 degree rule is when the camera must stay on one side or the other of an imaginary line, and must be kept within a field of 180 degrees. It is sometimes seen as very confusing, since the directions established for the viewer is changed. An example of this would be like watching a football game, with the runner going to the right, and all of a sudden we cut to him running to the left. It would make the viewer wonder if he was running the right way or not.