How is arthur radley a strong, productive adult?

Answer: Arthur was a very rare sort of person; quiet, yet caring, misunderstood like most people can be, but how many are caring enough to keep watch over 2 small children, and put himself in mortal danger in order to do whatever was necessary to protect these 2 children from a hate filled drunkard who one could see had badly beaten his own child? Who is so kind to offer up his own life to save others and not only did not seek praise or reward, but shun it? This is an exceptional person. He saves the children, puts himself in a very possibly bad legal position, but it was the right thing to do.

So many people would have never been on the spot, not taken a chance, nor fought a likely drunken man holding a large knife, a strong man made so by working manual labor, and at the end - taken "doing the right thing" as his desired reward.