As a previous poster mentioned, for the earth to stop and change rotational direction it would require immense forces that would probably tear the planet apart if performed over a short period of time. However, the earth could change rotational direction as viewed by an observer off planet if, the poles were to physically flip while the rotation remained constant. That would produce a sun that rises in the west and sets in the east. And if you don't believe me, spin a ball and turn it upside down. Now the real problem is what could cause a physical inversion of the planet, which I can only imagine would be an extremely powerful magnetic field, since it is unlikely that the gravitational field of a passing planet could change our rotational orientation. So, if the sun sent out a dense and large plasma cloud from a solar flare that contained a sufficiently strong magnetic field of opposing orientation to earth's, it is possible we could be physically flipped without losing much rotational speed and then the sun would rise in the west. That would be a helluva ride to be sure!