What tense situation occurs at the county jail? How does scout help her father in this scene?

Atticus is sitting outside of the the jail in an effort to protect Tom Robinson. He's heard that some men are going to try and lynch Tom, and he's not going to let that happen. Scout and Jem don't know where their father is, so they go to look for Atticus at his office, and then finally spy him sitting outside the county jail. The children stay a safe distance away so Atticus won't notice them. Jem feels reassured knowing where his father is, but as they are about to head home, four old cars come into town. A shadowy group of men emerges. Atticus informs them that the sheriff is nearby, but they counter that they called him into the woods on false pretenses. Atticus still seems unperturbed. Suddenly Scout runs out into the circle, but is taken aback when she realizes that these men are strangers to her. Atticus orders the children to go home, but Jem refuses. One man picks up Jem by the collar, and Scout kicks the man in the groin. Jem still refuses to leave.

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." The men decide to disperse, and go home in their cars.