In folklore, spitting averts evil and protects one against Ghosts, witches, and evil spirits. When one encounters a ghost, the wisdom goes, one must spit on the ground in front of it and demand, “In the name of the Lord, what do you want?” The spittle supposedly prevents the ghost from harming the individual.
SOURCE:
The Encyclopedia of Ghosts and Spirits– Written by Rosemary Ellen Guiley – September 1, 2007