From Longman Dictionary of Contemporary Englishspitballspit‧ball /ˈspɪtbɔːl $ -bɒːl/ noun [countable] American English a small piece of paper that children roll into a ball and then spit or throw at each other
Examples from the Corpus
spitball• My memos are spitballs in the face of the faceless monolith where I work.• The Operations students - the field men - are called spitballs around here.• I checked around for spitballs and paper wads.• The other buildings are schoolrooms and a gymnasium for the spitballs and gut-men.• Anna said they are the ones who score low grades and throw spitballs in class. 