In To Kill a Mockingbird, Atticus faces two different groups of men at the jail where Tom Robinson is being held for the alleged rape of Mayella Ewell.
The group that approaches the jail are made up of two kinds of men, literally two separate groups.
One group is like Tim Johnson, the rabid dog in the story. They are filled with racial prejudice and hate, and want nothing more than to kill Tom without benefit of a trial.
Though it is difficult to sense a difference in any of the men that descend on the jail, it is actually Scout's words that bring the distinction between the groups to light.
The second group is made up of men who are frightened about how their world is changing. One of their own (a white man) has accused a black man of a serious crime. They are probably torn between looking for immediate "justice," and listening to the case and the evidence to prove Tom's innocence or guilt. They are not bad men, per se, but they become caught up in the mob's mentality.
However, when Scout spots Mr. Cunningham in the group and asks after his son Walter, a friend, she says, from school, Scout clears Mr. Cunningham's "vision" to see himself in a more civilized light by bringing to his mind the picture of his son. In being humanized in this way, Mr. Cunningham responds to Scout, another innocent child, and directs the rest of the men to leave. Those like Cunningham follow him. Those who cannot see the human side of the situation most probably leave because they have lost the strength in numbers with which they arrived, and therefore, have lost their power to take Tom forcibly from the jail.