As usual, Hadit has it! Witchcraft is the study and application of the magic in nature.It is a search for knowledge. How the Earth works.How the Universe works. How Life,itself, works. It is certainly not a religion! Many people,from many religions,practise witchcraft.
If you are a witch who also believes in a Deity, then you are following a religion. I have been a witch for many years. Yet I do not believe in anything supernatural.