Source : Webster's Revised Unabridged Dictionary (1913)

Spitball \Spit"ball`\, n.
   Paper chewed, and rolled into a ball, to be thrown as a
   missile.

Source : WordNet®

spitball
     n 1: a projectile made by chewing a piece of paper and shaping it
          into a sphere
     2: an illegal pitch in which a foreign substance (spit or
        Vaseline) is applied to the ball by the pitcher before he
        throws it [syn: {spitter}]