At the beginning of chapter 10, Scout elaborates on the various reasons she and Jem are embarrassed by their father. Scout mentions that Atticus is a "feeble" man, who is nearly fifty and is not physically active like many of their friends' fathers. Atticus also does not have an interesting job like driving a dump truck or working on a farm. Scout also laments the fact that Atticus wears glasses and does not seem very manly. According to Scout, Atticus is a relatively boring person, who prefers to read instead of playing poker, fishing, or drinking with the other men in the community.
Later in the chapter, Scout and Jem are astonished to discover that their father is an expert marksman after he shoots and kills a rabid dog named Tim Johnson on the first shot. They are also perplexed to know why Atticus never told them that he was an expert marksman, who earned the nickname Ol‘ One-Shot as an adolescent.
Scout the narrator opens Chapter 10 of To Kill a Mockingbird by describing Atticus as old and feeble:
Atticus was feeble: he was nearly fifty. When Jem and I asked him why he was so old, he said he got started late, which we felt reflected upon his abilities and manliness. (Ch. 10)
In other words, Scout and Jem are embarrassed by the fact that Atticus is older than the fathers of other kids their age and feel he is feeble because of his age.
In their eyes, Atticus's feebleness is revealed in many ways. First, Atticus is unable to play football with Jem, which severely disappoints Jem since he loves football so much. Atticus is able to play keep-away, but whenever asked to play tackle football, Atticus replies, "I'm too old for that, son." Second, Scout feels his feebleness is reflected in his boring job. In Scout's eyes, Atticus doesn't do anything interesting like "drive a dump-truck for the county," be a sheriff, a farmer, or work in a garage. All Atticus does is work in an office, which is not "anything that could possibly arouse the admiration of anyone."
However, as the chapter progresses, the children soon learn Atticus has talents he keeps secret, such as excellent marksmanship. As the novel progresses, the children learn just how admirable Atticus's job as a lawyer truly can be.