Walter Matthau as Morris Buttermaker, coach of the Bears: A drunken, loud, ex-professional baseball pitcher and part-time pool cleaner, who drives a rundown green Cadillac convertible.
Tatum O'Neal as Amanda Whurlitzer, the 11-year-old star pitcher for the Bears who feels insecure about her tomboy image. She is recruited by Buttermaker to help the team start winning. She is no-nonsense and a great pitcher who was taught by Buttermaker when she was young. The boys grow to be very protective of her, picking a fight with their rivals during the championship game when Amanda is kicked in the chest. Her mother is Buttermaker's ex-girlfriend, and Amanda looks to him as a father figure. Amanda and Tanner often butt heads but respect each other. She also has a secret crush on Kelly.
- Jackie Earle Haley as Kelly Leak, the local troublemaker who smokes and rides a mini Harley-Davidson motorcycle. Kelly is also the best athlete in the neighborhood. At first, he does not want to join the team when Amanda attempts to recruit him, but he changes his mind when Coach Turner threatens him. He alternates between left and center field, and has a crush on Amanda. After joining the team, he forms close friendships with Tanner, Ahmad and Ogilvie.
Chris Barnes as Tanner Boyle, the short-tempered shortstop with a Napoleon complex; after suffering a horrible loss in their first game, he picks a fight with the entire seventh grade from the boys' middle school (and loses). He tends to curse more than the others, and initially insults and bullies Timmy before realizing that he is treating Timmy no better than the kids from their rival team. He becomes protective of Timmy, leading to an unlikely friendship between them. He is also close friends with Ahmad.
Erin Blunt as Ahmad Abdul-Rahim, who plays in the outfield, is liked by everyone on the team and adores Hank Aaron; Ahmad strips off his uniform in shame after committing several errors in the Bears' first game, but is convinced to return to the team by Buttermaker, and is often used for bunts due to his speed. He is shown to be close friends with Tanner, and often has to pull Tanner away from fights.
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- Gary Lee Cavagnaro as Mike Engelberg, an overweight boy who plays catcher; a great hitter, he frequently teases Tanner about his size. He breaks Buttermaker's windshield with a baseball at the first practice. He has a deep rivalry with Yankee pitcher Joey, causing them to throw insults at each other.
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- Alfred W. Lutter as Alfred Ogilvie, a bookworm who memorizes baseball statistics. He is mostly a bench-warmer who assists Buttermaker with defensive strategy. A backup outfielder and first baseman, but reluctant to play because he feels that he is one of the lesser-skilled players on the team.
- David Stambaugh as Toby Whitewood, an unassuming boy who plays first base. He knows about the other players' personalities, is intelligent and well-spoken, and occasionally speaks on behalf of the team. He is the son of councilman Bob Whitewood, who secretly paid Buttermaker to coach the team.
- Quinn Smith as Timmy Lupus, initially described by Tanner as a "booger-eating spaz", plays right field and is considered to be the worst player on the team—if not the entire league—but he surprises everyone in the championship game by making a key play to keep the Bears in the game. He is the most quiet and shy player, but shows the ability to prepare a martini for Coach Buttermaker while the team is assisting him with cleaning pools.
- Jaime Escobedo as Jose Aguilar, Miguel's older brother who plays second base and does not speak English.
- George Gonzales as Miguel Aguilar, Jose's younger brother who plays mostly right field and does not speak English. He is so short that the strike zone is practically nonexistent.
- David Pollock as Rudi Stein, a nervous relief pitcher with glasses who is a terrible hitter. At times, he is asked by Coach Buttermaker to purposely get hit by pitches to get on base. He is also a backup outfielder.
- Brett Marx as Jimmy Feldman, a fairly quiet third baseman with curly blond hair.
- Scott Firestone as Regi Tower, a fairly quiet, red-headed infielder whose father vocally attends practices and games. He plays first base.
- Brandon Cruz as Joey Turner, the star pitcher for the Yankees and coach Roy Turner's son. He has a rivalry with Engelberg and regularly bullies Tanner and Timmy. He nearly beans Engelberg, which results in his father slapping him. In response, Joey holds a ground ball that Engelberg hits to him, allowing an inside-the-park home run. He drops the ball at his father's feet and quits the team.