During the act of fellatio, the one who is sucking
will suck one of the sides of the suckee's penis up and down, thus side-shafting. Side shafting may lead to what is known as the 'Ultimatum of Pleasure' which is the
pre-
ejaculation stage.
During a
blowjob, the female may or may not side-shaft the man depending on how experienced she is or how good she wants the
blowjob to be for the male.
Side-shafting can occur during a session of getting your
cock sucked well.