spit something on(to) something
to expel something from the mouth onto something. You shouldn't spit your gum onto the sidewalk! Don't spit your gum on the pavement.
spit (up)on someone or something
1. to eject spit onto someone or something. (Upon is formal and less commonly used than on.) The angry crowd spit on the convict. Don't spit on the sidewalk.
2. to spew spittle onto someone or something while talking. (Upon is formal and less commonly used than on.) I always have a fear of accidentally spitting on someone in the first row while I am talking. I regret spitting on you, but it was an accident.