Henry is a highly skilled but chronically anxious shortstop from a small town in South Dakota. Small for his age and lacking natural social confidence, he relies entirely on rigorous physical discipline and the philosophical teachings of his idol, Aparicio Rodriguez. Recruited to play for Westish College, Henry struggles to acclimate to the intimidating academic environment and the immense expectations placed on his athletic performance.

Schwartz is the burly, authoritative catcher and captain of the Westish Harpooners baseball team. Operating more like a coach than a student, he orchestrates Henry's recruitment and enforces a punishing workout regimen for his teammates. Beneath his confident exterior, Schwartz wrestles with the physical toll of chronic sports injuries and his fears of inadequacy regarding his academic and professional future.

Guert is the esteemed president of Westish College and a prominent scholar of 19th-century literature, particularly the works of Herman Melville. Having returned to his alma mater to lead the institution, he maintains a carefully curated image of academic respectability. A former womanizer during his Harvard years, Guert finds his strict professional boundaries challenged when he begins questioning his desires and identity.

Pella is Guert's daughter, who previously dropped out of high school and abandoned an Ivy League education to marry an older architect. Returning to her father's campus, she attempts to rebuild her identity from scratch by taking an entry-level job in the cafeteria. She is fiercely independent but struggles with feelings of regret and a desire to escape her controlling husband.

Owen is a confident, openly gay student and member of the Westish baseball team. Nicknamed "Buddha" for his unshakeable calm, he reads books in the dugout during games and leads an environmentalist student group on campus. He is highly self-assured, refusing to apologize for his identity, which makes him a grounding force for the more anxious characters around him.

David is a successful, 31-year-old architect who married Pella when she was still a teenager. He is calculating and deeply focused on maintaining his authority within his marriage. When Pella leaves him, he travels to Wisconsin, utilizing manipulative tactics and gaslighting to try and force her return to their previous dynamic.

Adam is an exceptional pitcher for the Westish Harpooners who frequently trains with Schwartz and Henry. He possesses a natural athleticism that attracts professional scouts, creating an undercurrent of competition among the team's top players.

Coach Cox leads the Westish College baseball program. While he holds the official title, he frequently defers to Schwartz's judgment regarding player development and team strategy, recognizing his captain's intense dedication to the game.

Sophie is Henry's younger sister, a high school sophomore living in their small hometown. She looks up to her brother but remains disconnected from the intense pressures he faces on the baseball field.

Genevieve is Owen's mother, a glamorous news anchor based in San Jose, California. She shares her son's striking physical features and possesses a direct, inquiring personality.

Chef Spirodocus manages the dining hall kitchen at Westish College. He takes pride in his culinary skills and becomes an unexpected mentor to Pella when she asks to work as a dishwasher.

Aparicio is a legendary professional shortstop and the author of The Art of Fielding. Though he exists primarily as a figure of mythic importance to Henry, his philosophical approach to baseball dictates the young player's entire existence.

Mrs. McAllister is President Affenlight's dutiful administrative assistant. She keeps the college office running smoothly and manages his increasingly erratic daily schedule.

Professor Eglantine teaches poetry at Westish College. The students respect the serious academic environment maintained in the classroom.

Contango is a friendly dog belonging to the Bremens, a local couple selling their home. The dog becomes a comforting presence for Guert as he contemplates a significant life transition.