Why does the gray wolf come into the Baxters' yard in The Yearling?
The gray wolf comes into the Baxters' yard because it is lonely and sick. It had plainly run into the Baxters' dog Rip before, and had returned for his companionship.
The great storm which had struck the area during the past fall had upset the balance of nature. A great pack of wolves, displaced by the flooding and starving because the plague has decimated their usual prey, had begun to terrorize the farms in a desperate quest for food. Penny and the other men in the area had rounded up the dangerous creatures in order to protect their families and their livestock. Most of the wolves had been eliminated; the gray wolf that comes to the yard in January is "almost certain the last one."
When Jody discovers the gray wolf, he is "romping with Rip in play." The two canines play silently, and Jody watches in fascination before calling Penny over to see too. Penny watches, without making a move for his gun. He sees that the wolf is "someway piteeful," a "pore thing, hurt and lonesome - come visitin' its nighest kin to pick a play." Noting the ragged condition of the wolf, Penny does not feel it is any threat to the Baxters or their livestock; he'd "not dream o' botherin' it." Sensing that it does not have long to live, Penny opts to let nature take its course and lets the wolf escape "to live out the rest of its life" (Chapter 28).