comment on the way Scout affects events without realizing it at the time in chapter 15

I think you might be referring to when the mob of men confronts Atticus in front of Tom Robinson's cell. Scout becomes interested in the men, who smell of "whiskey and pigpen" and are dressed in heavy dark clothes despite the summer night. Looking for a friendly face in the group, she recognizes Mr. Cunningham, the father of Walter from her class at school. Trying to be cordial, she innocently begins to talk to Mr. Cunningham about how Walter is a good boy, and recounts how they invited him home for dinner one day, and asks Mr. Cunningham to say hello to his son for her. Then she tries to engage him on the topic of his entailment, which she heard her father mention once, but notices that everyone is staring at her. Mr. Cunningham bends down to Scout's height and says, "I'll tell him you say hey, little lady."  Scouts innocence diffueses a tense situation that was filled with the threat of violence.