A fast-running, frequently angry teenager living in the low-income Glass Manor neighborhood. He struggles heavily with the trauma of his father's past violence, which manifests in a short temper and physical fights at school. Despite his tough exterior and sensitivity regarding his clothes, he is deeply protective of his hardworking mother and shows genuine compassion for others facing ridicule. Joining a local track team gives him an unexpected outlet for his undirected energy.

The demanding coach of the Defenders track team who also works as a local taxi driver. A former Olympic gold medalist, he sees past Castle's angry exterior because he recognizes the signs of a troubled upbringing. He acts as a firm father figure to the young athletes, using the discipline of running to help them face their personal struggles rather than flee from them.

A confident, incredibly fast sprinter on the Defenders track team who wears expensive athletic gear. Because he has albinism, he experiences bullying and masks his deep insecurities with a boastful, occasionally arrogant attitude. He initially clashes with Castle during tryouts before they begin to develop a mutual respect as athletes.

A large, mild-mannered distance runner who lives in an affluent neighborhood. He lacks natural sprinting ability but pushes himself relentlessly through endurance exercises. He participates in the sport largely due to intense family pressure following the death of his mother.

A tall, fast sprinter and the only female newcomer on the Defenders track team. She runs for deeply personal reasons related to her biological mother's health struggles. She is kind and perceptive, quickly offering encouragement to Castle when he embarrasses himself early in his training.

Castle's hardworking mother who studies online and works at a hospital cafeteria to support her son. She prioritizes Castle's education and safety above all else, only allowing him to join the track team if he maintains good behavior and avoids fighting.

Castle's father, currently serving a ten-year prison sentence. His terrifying, violent actions while intoxicated fundamentally shattered his family and left his son with severe anxiety and behavioral issues.

The local store owner who acts as a dependable, caring figure in Castle's life. He famously sheltered Castle and his mother in his storeroom during a terrifying domestic violence incident years ago.

A school bully who continuously mocks Castle for living in Glass Manor and wearing cheap clothes. His antagonism triggers Castle's anger, leading to a physical altercation that threatens Castle's spot on the track team.

The school principal who handles disciplinary issues. He shows leniency after hearing Castle's side of the cafeteria fight, deciding on a brief suspension rather than a harsher punishment.

The assistant coach of the Defenders track team. She works alongside Coach Brodie and specifically oversees and praises the distance runners like Sunny.

A classmate of Castle's who loudly laughs at his attempt to alter his high-top sneakers with scissors, prompting the rest of the class to join in and causing Castle to flee the school.

One of Castle's few friends at school, present during the stressful cafeteria fight.

Another of Castle's school friends who sits with him in the cafeteria before trouble starts.

An employee at the local sporting goods store who is present when Castle decides to shoplift a pair of expensive silver running shoes.

Castle's supportive aunt, who comes over to cheer for him as he prepares for his inaugural race with the Defenders.

Castle's cousin who joins the extended family in supporting Castle at his track meet.

Coach Brodie's wife, who attends the track meets to support the team.

Coach Brodie and Margo's infant son.

Sunny's demanding father who pressures his son to run track in order to fulfill the athletic ambitions of Sunny's late mother.

Patty's biological mother, who gave her up for adoption due to severe health struggles with diabetes that resulted in the amputation of her legs.

Coach Brodie's late father, an abusive man whose struggles deeply shaped Coach's childhood trauma and eventual path to success.

A veteran sprinter on the Defenders track team who helps lead the newer runners through their training routines.

A runner on the Defenders team who shows casual kindness to Castle during a grueling practice break.