"Million Dollar Baby" is famous for its dramatic shift in tone and plot, which re-contextualizes the entire film. For its first two-thirds, it masterfully builds the narrative of a classic underdog sports story. Maggie's rise from poverty, her bond with the reluctant Frankie, and her string of knockout victories all follow a familiar and uplifting trajectory. The hidden meaning that becomes clear only after this point is that the film was never truly about boxing; it was a character study about love, loss, and the nature of mercy. Boxing was merely the vehicle for Maggie to achieve her life's dream in the short time she had.
The turning point is the championship fight against the notoriously dirty fighter, Billie 'The Blue Bear'. After a round has ended, Billie lands an illegal sucker punch, knocking Maggie onto her corner stool. The impact breaks her neck, leaving her a ventilator-dependent quadriplegic. This is the film's great reveal: it is not a story about winning a title, but about the aftermath of a dream realized and then brutally cut short.
In the hospital, Maggie's suffering is compounded by a visit from her family, whose only concern is getting her to sign over her assets. After they leave, she asks Frankie to help her die, a request he initially refuses. After developing bedsores that lead to a leg amputation, and after a failed suicide attempt where she bites her own tongue, Maggie's resolve strengthens. Frankie, torn between his Catholic faith and his love for her, finally agrees. In the film's climax, he sneaks into her room, tells her that "Mo Cuishle" means "my darling, my blood," and administers a fatal injection of adrenaline before disappearing forever. The final reveal is that Scrap's narration has been a letter to Frankie's estranged daughter, telling her "what kind of man your father was," bringing the theme of redemption full circle.