Definitions for "spitball"
Paper chewed, and rolled into a ball, to be thrown as a missile; -- a childish prank.
A pitched ball in throwing which the pitcher grips the ball between two, or three, fingers on one side (which is made slippery, as by saliva) and the thumb on the other side, and delivers it so that it slips off the fingers with the least possible friction; -- also called spitter. When pitched directly overhand a spit ball darts downward, when pitched with the arm extended sidewise it darts down and out. The use of such a pitch is against the rules of professional baseball.
a projectile made by chewing a piece of paper and shaping it into a sphere
to toss ideas around with no expectation of them coming to pass, to brainstorm.