A simile is a comparison of two unalike things where one is said to be like or as the other. For example, when Sarty and his father leave the makeshift courtroom, a local boy lashes out and punches Sarty. The narrator says, "Again he could not see, whirling; there was a face in a red haze, moonlike, bigger than the full moon [...]." The face of the older boy who strikes the young Sarty is compared to the moon, it seems so big to Sarty, and yet Sarty actually does try to give chase before his father calls him back. Sarty wants to be loyal, but his father is terrible.
Later, the narrator describes Ab Snopes, Sarty's father, as having a "wolflike independence." We often think of independence as a good thing, but, in Abner's case, there's a danger present: brutality. He does not seem to really love his wife or children, and he can be terrible cruel, animal, and unfeeling towards them. Later, just before Ab hits Sarty, the narrator describes his voice as being "harsh like tin and without heat like tin": Ab is cold and emotionless, even when speaking to his son.
When Sarty follows his father up the path to Miss Lula's house, the narrator describes Ab an "the ironlike black coat," associating Ab with a metal that is known to be rigid and unyielding. Sarty hears his father's footfall "with clocklike finality," further indicating how inflexible and inexorable his father is. When Sarty looks at his father's hand, it is "like a curled claw," another simile that emphasizes Ab's cruel nature. When Ab tracks mud and manure onto the pale rug in the hallway, he does so with "machinelike deliberation," yet another simile that emphasizes his lack of humanity.