A "vulture back" in fantasy football is a running back that used exclusively in goal line situations in which the offense needs just a few yards to score a touchdown. The term is derived from the running back's tendency to "vulture" touchdown runs from the primary running back that was on the field for the majority of the offensive drive.
Vulture backs are often strong and stout running backs with physical, uphill running tendencies. These characteristics make them extremely useful for short touchdown runs, enabling them to lower the shoulder and achieve the extra push required to cross the goal line.
Fantasy owners dread teams that use vulture backs. This is because most fantasy owners draft primary running backs that are on the field for the bulk of an offense's run plays. The nature of the scoring system in most leagues (1 point per every 10 yards rushing, 6 points for every rushing touchdown) dictates that running backs generally need to score touchdowns in order to post a high number of fantasy points. Thus, if a team's primary running back rushes for 40 yards on a drive but is replaced by a vulture back who goes on to score a touchdown near the goal line, the fantasy manager only receives 4 points as opposed to the 10 points that would have been recorded if the primary back had scored the touchdown.