Sheriff Tate and the other men who congregate in Atticus's front yard are worried because they have just learned that Tom will be moved to the local county jail the following day. Tate recognizes that there may be surprises. "I don't look for any trouble, but I can't guarantee there won't be any...," he tells Atticus. Link Deas responds that it's not the people of Maycomb that are "up to anything, it's that Old Sarum bunch I'm worried about..." The men are concerned that Tom may not be safe in the jail with just Sheriff Tate on guard, and their suspicions prove to be true the next evening. First, Tate is lured away on "a snipe hunt," forcing Atticus to stand alone outside the jail. Just as Link Deas predicted, it is a group of Old Sarum men (including several of the Cunningham clan) who show up at what they expect will be an undefended jail, intent on taking Tom by force and lynching him.
In chapter 15, Heck Tate, Link Deas, and others who are concerned about the Old Sarum bunch causing trouble go to Atticus for a discussion. They feel that once Tom Robinson is moved to the Maycomb jail the night before his trial, there might be a problem because the Cunninghams could do something crazy. Atticus doesn't believe that there should be any problem holding Tom for one night in their town jail, but the others say that once the Cunninghams get liquored up, they may do something problematic. Link Deas asks the sheriff if they could have a "change of venue," but Tate answers, "Not much point in that, now is it?" (145). With one night to go before the trial, it is better for everyone if Tom can just stay in town for the night, but the town doesn't want a lynching, either.
Atticus says that the Cunninghams go to church on Sundays, so they shouldn't be drinking and out doing crazy things. Someone in the crowd says, "This is a special occasion, though" (145). After much discussion, they decide to keep Tom Robinson there, but a proactive and defensive plan is created. Atticus plans to sit in front of the jail while being covered by Mr. Underwood's shotgun the night before the trial. So, initially, the group of men go to Atticus with their concerns, and it is Link Deas who suggests not having Tom in town the night before the trial. The plan they come up with turns out for the best and keeps Tom in Maycomb for his trial.
Since Harper Lee’s novel To Kill a Mockingbird is a story about overcoming the sins of prejudice and intolerance, we can assume that Heck Tate and his men are worried about a possible lynching when they discuss the fact that Tom Robinson is being held at a local jail.
Their fear is very well founded. Lynching happened in the South all too often. Angry white crowds were known to drag accused African-American criminals out of jail before they had ever been tried and hang them off buildings or from trees.
The New York Times recently published an article by Campbell Robertson titled “History of Lynching in the South Documents Nearly 4,000 Names.” The article cites a report by the Equal Justice Initiative in Montgomery, Alabama, five years in the making, that recognizes 3,959 lynchings in 12 southern states from 1877- 1950. These acts of vigilantism were well known to the readers of To Kill a Mockingbird, which was published in 1960 and set in the 1930's.