The incident occurs in Chapter Twelve. The boy who is beaten up is Nathan. The beating is carried out by other boys whom he had considered friends. The crime had been that the fact that his father had gone to work for Shomer, the tax collector. To work for the Romans in this fashion was akin to complete betrayal of the Jews.
Nathan tries to explain his father's position. The family's crops had been eaten by locusts the previous year, leaving his father unable to meet the taxes on the property. His only choice would have been to sell his sister, but he "was too soft hearted."