Why did the neighbors gather in the Finches' front yard in Chapter 15 of To Kill a Mockingbird?
The more prominent men of Maycomb assemble in the Finch front yard in order to speak privately to Atticus about getting a change of venue for the trial of Tom Robinson in order to prevent a lynching or other problems.
This meeting of the businessmen and sheriff is a "let this cup pass" moment much like the one between Atticus and his brother Jack in Chapter 9 in which Jack asks Atticus "how bad" the forthcoming trial of Tom will be. As he speaks privately to his brother, Jack asks Atticus if he can avoid being involved--"Let this cup pass from you, eh?"
The Maycomb men who have much invested in their town have their worries voiced by Mr. Link Deas who observes that the townspeople present no problem; however "It's that Old Sarum bunch I'm worried about...." Clearly, this is a "[L]et this cup pass" moment for the assembled men. But, Atticus is stalwart in his determination to provide Tom his rights under the Constitution:
"Link, that boy might go to the chair, but he's not going till the truth's told....And you know what the truth is."
Truly, this meeting with the townsmen is another illustration of the integrity of Atticus Finch, who is willing to risk his own personal safety in order to provide justice under the law for the innocent Tom Robinson.
In Maycomb, grown men stood outside in the front yard for only two reasons: death and politics. I wondered who had died. (Chapter 15)
But no one had died. Led by Sheriff Tate, the group of men who suddenly appeared in Atticus's yard were all friends. They decided to speak outside, away from the ears of Atticus's children and Aunt Alexandra. They had come to warn Atticus about Tom's move to the county jail the next day.
... Mr. Tate was saying, "I don't look for any trouble, but I can't guarantee there won't be any..." (Chapter 15)
Link Deas was worried about " 'that Old Sarum bunch,' "--the men who would eventually show up in the form of a lynch mob the following night. He also scolded Atticus for deciding to defend Tom in the first place. Atticus didn't believe trouble was forthcoming, telling the group that the Old Sarum crowd rarely got drunk on Sundays. When Jem suddenly screamed to Atticus about a nonexistent phone call, the "men jumped a little and scattered." Atticus told Jem to answer it, and "Laughter broke them up." The tense meeting dissolved, and Atticus had to explain to Jem and Scout that the men were only his friends, and not a "gang" who " 'wanted to get you...' "