Circles are everywhere, top of a coffee cup, a wheel, DVDs, ashtrays and so on. The goal of the contest is to show us perfect circles and they must be the main focus of the shot. The circle itself can be shot from any angle, so we do not need a top view.
An ellipse is considered off-theme. A perfect sphere is on-theme. The term 'perfect circle' means it has to be a smooth circle, objects made out of multiple parts (like a soccerball or tennisball) and make a reasonable smooth circle that way are allowed.
By doubt if the subject is a perfect circle mods can ask for a 2nd shot (in the SBS) of the same object which shows the subject is a perfect circle. When asked you must comply.
This is up to the mod, members can not ask for this in the comments (use the red flags!)