Definition of sour balls:
(n) :
a
ball of
snow, usually one made in the hand and thrown for amusement in a
snowball fight; also a larger ball of snow made by rolling a snowball around in snow that sticks to it and increases its diameter; a
cocktail made from
lemonade and
advocaat
(v) :
to rapidly grow out of proportion or control; to play at throwing snowballs
"the high unemployment rates quickly snowballed into a major budget problem for the government."