The act of slapping ones friend across the face with a hand that recently resided upon your sack and taint. Best performed after a night of dancing and drinking. Caution, execution of a successful fast ball will require a retreat with due haste as the recipient of the fast ball WILL retaliate with extreme violence. Best executed whilst already running from your victim.
Person 1: I can't believe you fast balled Eddie! Didn't you remember he's our ride home?