In 1st and 2nd editions of Vampire: The Masquerade, Sabbat vampires were created through an initiation ceremony. Sabbat initiates were Embraced by their sire, bashed over the head with a shovel (to knock them unconscious before they Frenzy), thrown in an open grave, and buried. The whelp then had to dig his way out of the grave, during which time he would be dogged with bizarre hallucinatory visions thanks to the Embrace's mystical properties. When (or if) the neonate emerged, he was completely stripped of his humanity and ready to learn how to be a Sabbat.
The Revised Edition Sabbat do not do this; while "shovelheading" is still a technique occasionally used (particularly for War Parties), most of the Sabbat clans are a bit more choosy about who they Embrace. Instead, "true" Sabbat still go through a rite of indoctrination, but it is not necessarily the shovelhead approach.