Ab is a man who has tried to impress his son with a sense of loyalty to family above all else. We see, early on, when Sarty considers:
... his father’s enemy (our enemy, he thought in that despair; ourn! Mine and hisn both! He’s my father!).
Sarty knows that his father would have him lie to the justice presiding over the case—“And I will have to do hit,” he thinks. He is, evidently, intimidated and even fearful of his father.
When Ab finally does speak, he says “something unprintable and vile” to the court and expresses his intention to move somewhere far away from these people. His voice, when he speaks to his son, is described as “harsh” and “cold,” even after Sarty is struck to the ground by another boy. Ab doesn’t even find it necessary to tell his family where they’re moving to next, and he is described as having a “wolf-like independence”—a somewhat inappropriate quality when one has a wife and children to support. Wolves are so potentially ruthless and savage and animal in nature. He even keeps “a shrewd fire” though his family is cold; it is evident that he does not harbor feelings of tenderness for them.
Sarty realizes the reason for the small fire must be his father’s war experiences and his need to hide “from all men, blue or gray,” because he was, evidently, stealing horses. He doesn’t quite realize that the fire “spoke to some deep mainspring of his father’s being.” The narrator does say that Ab’s “wolf-like independence and even courage when the advantage was at least neutral” was something that “impressed strangers.” If we can consider these good qualities, then he does possess them.