Because of his reclusive life and the mystery surrounding it, Boo Radley is very vulnerable, very open to attack. For instance, at the beginning of Scout's narrative, in Chapter 3 as the children bring Walter home for lunch, Jem proudly boasts, "A haint lives there" as he points out the Radley house across from theirs. Walter tells the Finch children that he nearly died from eating Radley pecans,
"...folks say he pizened 'em and put 'em over on the school side of the fence."
Other superstitious beliefs exist about Boo as Scout narrates in Chapter 1. Supposedly, Boo is a "malevolent phantom" who goes out at night when the moon is down and peeps into windows, such as that owned by Miss Stephanie Crawford. "When people's azaleas froze in a cold snap, it was because he had breathed on them"; if a Negro came near the Radley house at night, he would cut across the street and whistle to calm himself as he walked. If anything out of the ordinary happened, it was thought to have been caused by Boo Radley.
Also in Chapter 1 Scout relates the many rumors that abound about Boo Radley, who has not come out of his house since he was arrested by the town beadle, Mr. Conner. According to Miss Stephanie, when the judge sentenced Arthur Radley to the boys state industrial school, his father promised the judge that he would make sure Arthur gave the town no more trouble. Boo Radley was never seen for fifteen years. Some said he once stabbed his father in the leg with a scissors as he passed by, and then merely resumed his activities.
Certainly, Boo Radley's vulnerability lies in the townspeople's not knowing Arthur Radley. This ignorance of the man leads to the superstitious beliefs that they possess. Therefore, when Boo finally comes out of his house, it is surreptitiously that he does so. In Chapter 6, one night when Dill and Jem go up to a Radley window on a dare, Mr. Radley hears them and comes out with his shotgun, which he fires. When Jem catches his pants on the barbed fence, he must take off his pants in order to escape. But, the next day when he returns, Jem finds them mended. Later, in Chapter 8, Boo fills a knothole with gifts for Jem and Scout, adding to the children's superstitious wonder about him.
Perhaps at no other time, though, is Arthur Radley more vulnerable than at the end of the narrative when this maladjusted, timid recluse bravely defends the chidren through whom he has lived vicariously. His courageous defense of Jem and Scout ends with the death of Bob Ewell, a death that Sheriff Tate concludes that is caused by Ewell's having fallen upon his own knife. When Atticus is not convinced, he tells the lawyer,
"I never heard tell that it's against the law for a citizen to do his utmost to prevent a crime from being committed...but maybe you'll say it's my duty to tell the town all about it and not hush it up. Know what'd happen then? All the ladies in Maycomb...would be knocking on his door bringing angel food cakes. To my way of think', Mr. Finch taking the one man who's done you and this town a great service an' draggin' him with his shy ways into the limelight--to me, that a sin. It's a sin and I'm not about to have it on my head. If it was any other man it'd be different. But not this man, Mr. Finch."
Clearly, Mr. Tate recognizes the vulnerability of Boo Radley who would be susceptible to the curious and those who would exploit his new found notoriety.