At the end of chapter 15, it states that "Mr. Underwood and a double-barreled shotgun were leaning out his window above The Maycomb Tribune office." Mr. Underwood said, "Had you covered all the time, Atticus." This is a relief, because the crowd had been pretty threatening, and if it hadn't been for Scout's innocent questions, things could have gotten violent.
As Atticus protects jailed Tom Robinson from an mob of vigilantes, Mr. Underwood, the owner of the Maycomb newspaper, is positioned from a second-story window with a double-barreled shotgun pointed at the angry men. When the lynch mob leaves, Atticus and the children discover Mr. Underwood as he says, “Had you covered all the time, Atticus.”
Ironically, Mr. Underwood does not make himself known to the mob. Some critics say it is because he was afraid of retaliation or of being shunned from society for protecting Atticus, a man who was defending a black "rapist." Mr. Underwood is also know to "despise" black people.
Mr. Underwood, the editor of the Maycomb Tribune, is holding a double-barreled shotgun and positioning it out the window of his office. Scout explains earlier that in his position as newspaper editor and writer, Mr. Underwood can report on
"the courthouse and jailhouse news simply by looking out his upstairs window." His office window looks directly out at the jail where the mob has gathered. After the mob disperses, Mr. Underwood tells Atticus that he had him "covered all the time."
In some senses, Scout also "covers" Atticus. She searches for someone in the mob who she knows, and when she realizes that she knows Mr. Cunningham, she speaks to him about his entailment, a legal issue related to land that Atticus is helping him with. She also speaks to Mr. Cunningham about his son, Walter, who attends school with Scout and who Scout and Jem brought home for dinner once. Reminding Mr. Cunningham of his son makes him embarrassed and causes him to think of himself as a father rather than as a member of a vigilante mob going after Tom Robinson. As a result, the energy goes out of the mob, and they disperse.
Mr. Underwood is actually the one who is covering him. He has a shotgun pointed at the men but they have no idea that he was there. After the mob leaves he tells Atticus that he had him covered, but he is also like the other men and he is not as accepting of colored folk as Atticus.