Which natural event is attributed to the spirits of the dead playing football with a walrus skull?

The natural event that is attributed to the spirits of the dead playing football with a walrus skull is Aurora borealis.
These northern lights, that often appear in the northernmost countries such as Scandinavia, Alaska, Greenland, and the Arctic, and in the distant past, when there was no technology or scientists to explain this phenomenon, people would say that they could see warriors and spirits in the sky, when in fact it was just Aurora borealis.