In To Kill a Mockingbird, Harper Lee uses Jem and Atticus Finch's favorite pastimes to deepen their characterization.
Jem's pastime is football, which Harper Lee reveals in the very first chapter of the book. The fact that Jem likes football reveals a couple of important aspects of his character. First, Jem is moving toward adulthood; he is leaving Scout's childish games behind and has chosen a more age-appropriate sport. Jem's preference of football also reveals that he is not afraid of conflict, since football is a highly competitive contact sport. You have to take personal risks at times, playing football. It also requires teamwork and discipline.
Atticus Finch was known as the best checker player in Maycomb; this reveals that he prefers strategy games and thinking critically to solve problems. He also plays a jew's harp (mouth organ) and is very good at shooting, earning him the name "One-shot Finch." Atticus' skill with the gun reveals that he has a steady hand and an attention to detail, both important characteristics in superior marksmanship. Atticus was also very well read.