In Chapter 2, Atticus explains to Scout that Walter Cunningham Sr. can not pay him for his services in money. So, he allows Walter to pay in any way he can. Atticus tells him to concentrate on his own problems and pay him back when he can:
“Let that be the least of your worries, Walter,” Atticus said.
Walter eventually pays him in goods such as stovewood, hickory nuts, and turnip greens.
At the end of Chapter 5, Atticus reprimands the children for making fun of Boo Radley.
“Son,” he said to Jem, “I’m going to tell you something and tell you one time: stop tormenting that man. That goes for the other two of you.”
Scout adds that if Arthur wanted to come out, he would on his own terms. (One of their goals is to lure Arthur outside.) Atticus knows that Arthur has had a troubled childhood and prefers to stay inside. He doesn't want his children, or Dill, to make Arthur's life any more difficult.
In Chapter 23, we learn that Bob Ewell has spit on Atticus at the post office. Bob then challenges Atticus to a fight and Atticus walks away saying he is too old to fight. Jem wonders why Atticus won't protect himself or fight back. Atticus replies that he understands why Bob retaliated in this way. Atticus had embarrassed Bob in court and this was Bob's way of getting back at him. Atticus gives Bob a pass on this for another reason. He concludes that if Bob has to take out his anger on someone, he would rather take the abuse than let Mayella or one of the Ewell children take it. This is Chapter 23, about two pages in. He shows understanding for Bob and compassion for Mayella and the Ewell children:
So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that’s something I’ll gladly take. He had to take it out on somebody and I’d rather it be me than that houseful of children out there.