Scapegoating, as it has come to be known, is when any one person or group is singled out and made to accept the blame for something that isn't their fault. It has its origins in the Old Testament of the Bible, when a goat was selected to bear all of the sins of the Israelites and then sent out into the wilderness, thus allowing all of the Israelites to be cleansed of sin. You can read more about it in Leviticus Chapter 16. In more modern examples, somebody is picked to be the scapegoat or the "fall guy," and as a result is made to bear the blame for mistakes that aren't necessarily his or her fault. A great example comes in the film Dead Poets Society, where Mr. Keating is made the scapegoat for Neil's death, even though he had very little responsibility for it.
In this excellent short story, the concept of the scapegoat relates to the horrific human sacrifice that the story ends with and the way in which each year, a member of the community is selected to be killed by the others to ensure a good and bountiful harvest. Consider the saying that Old Man Warner remembers that is absolutely crucial to this: "Lottery in June, corn be heavy soon." We can see therefore how the concept of scapegoating applies to this story. One member of the community is selected to be the metaphorical scapegoat, bearing all of the sins of the community. This scapegoat is then cruelly killed as a blood sacrifice to expiate the wrath of the gods and give the village a good harvest.