While growing up in Waterbury, Connecticut, young Jimmy Piersall dreams of becoming a major league baseball player with the Boston Red Sox, a dream he shares with his father John. Though he has just been fired from his job at the local bakery, John, an ex-ball player who never made it to the big leagues, is more interested in playing catch with his son than looking for a new job. Years later, Jimmy becomes the star of his local high school baseball team, leading Laurel to the state championship. Instead of congratulating his son, however, John chastises Jimmy for a few minor mental errors. After learning that the Red Sox are interested in Jimmy, father and son spend the winter sharpening the young Piersall's baseball skills, but all their hard work nearly goes to waste when Jimmy breaks his ankle ice staking with some friends. Though his ankle is still not completely healed, Jimmy returns to his high school team and hits an inside-the-park home run to win a game. The visiting Red Sox scouts are sufficiently impressed with Jimmy that he is offered a contract and assigned to Boston's minor league team in Scranton, Pennsylvania. While working out with his new team, the shy Jimmy literally runs into a young nurse named Mary Teevan. After inviting himself over to her apartment for dinner, Jimmy soon begins dating Mary. Following Scranton's league championship, Jimmy proposes to Mary, while warning her that life as the wife of a struggling ball player has many drawbacks. Jimmy's jubilation over his engagement is short-lived, however, as he nearly has a nervous breakdown when he overhears a radio announcer criticizing his play. Once back in Waterbury for the winter, Jimmy learns the Red Sox have decided to keep him in the minors due to his low batting average and reassigned him to their Louisville team. There, Jimmy celebrates the birth of his daughter Eileen with an eleven-game hitting streak. After being named the top outfielder on the Louisville team, Jimmy once again returns home to Waterbury, where Mary has purchased a new house, but a suddenly nervous Jimmy questions whether they can afford it. The next spring, Jimmy is finally called up by the Red Sox, but Joe Cronin, their manager, tells Jimmy that they want him to be the team's shortstop, a position he has never played before. Though Jimmy questions Cronin's decision, John is simply elated that his son has finally made it to the major leagues and tells Jimmy that he can quickly adjust to shortstop with "a little hard work." Jimmy becomes convinced, however, that he can never play the new position, and that the Red Sox and Cronin are trying to destroy his career. While Mary wants her husband to get medical help, John insists that his son go to the Red Sox's spring training camp in Sarasota, Florida. Once the regular season begins, Jimmy becomes the talk of the sports pages because of his bizarre on-field antics. After getting into a fight with one of his teammates, Jimmy is suspended from the team by Cronin, but John convinces Cronin to reinstate Jimmy and move him to the outfield. After hitting a home run against the Chicago White Sox, Jimmy suffers a nervous breakdown and has to be forcibly removed from the field. Jimmy is then committed to a state mental hospital, where he is placed under the care of Dr. Brown, a psychiatrist. Three weeks later, Brown tells Mary that there has been little progress in Jimmy's condition and suggests electric shock therapy. A breakthrough finally occurs when Mary is allowed to visit Jimmy, and he tells his wife how Cronin is responsible for his condition. Under analysis by Brown, however, Jimmy learns that his problems stem from his relationship with his domineering father, whom he feels he has never been able to satisfy. Later, John meets with Brown and insists the doctor release his son, but Brown informs him that Jimmy is not well enough to see his father, let alone leave the hospital. Nevertheless, John sneaks into his son's hospital room and tries to convince him to go home with him. Much to his father's shock, Jimmy stands up to John and orders him to leave. Later, Jimmy tells Brown that he wanted to kill his father, but the psychiatrist assures him that everyone has irrational impulses and the important thing is that he did not act upon them. Brown then tells Jimmy that he has always been living his father's dream, not pursuing his own desires. Realizing he still wants to be a ball player, Jimmy works hard to get back into shape, both mentally and physically, and despite the long odds, he is in a Red Sox uniform on opening day the very next season. As he prepares to take the field, Mary tells him that she is frightened, but Jimmy tells her it is "okay," as he is scared, too.