Can crop circles be square?
A crop circle is a sizable pattern created by the flattening of a crop such as wheat, barley, rye, maize, or rapeseed. Crop circles are also referred to as crop formations, because they are not always circular in shape.
Based on Wikipedia's definition, the answer is yes since a square is a "sizable pattern."
If your definition is more strict (i.e. focusing on the word circle) than Wikipedia's definition, then the answer is probably no because a circle cannot be a square and vice versa.