Brewer's: Spitting for Luck
Boys often spit on a piece of money given to them for luck. Boxers spit upon their hands for luck Fishwomen not unfrequently spit upon their hansel (i.e. the first money they take) for luck. Spitting was a charm against fascination among the ancient Greeks and Romans. Pliny says it averted witcheraft, and availed in giving to an enemy a shrewder blow.
Thrice on my breast I spit to guard me safe From fascinating charms.