Question: Where did the superstition knock on wood come from?
Disambiguated questions and answers: question: Where did the superstition knock on wood because of protection from supernatural beings come from?
Where did the superstition knock on wood to distract spirits come from?
From what object did the superstition knock on wood come from?
What is the more modern theory for where the superstition knock on wood come from?
answer: Celtic or German folklore
Pagans
wooden crucifixes
a form of tag called "Tiggy Touchwood"
Natural Questions answer: German folklore (from the Wikipedia article "Knocking on wood")