Continuity mistake: When Maggie is first shown in her hospital bed, you see her left eye is closed and swollen from the fight. Then, you see her left eye normal, then it goes back to swollen and shut. (01:33:20)
Continuity mistake: In Maggie's first fight (when Frankie isn't her manager), she comes off after the first round and takes her mouthpiece out. After talking to the manager, she gets back up to enter the ring without putting it back in, but when the bell rings she has it in again.
Continuity mistake: When Maggie is talking to Frankie in the gym bleachers, discussing Frankie's daughter, Maggie's ponytail keeps shifting from behind her back, to over her shoulder, and back again.
Audio problem: During any fight when people are yelling "Mo cuishle", watch the spectators around and you'll notice that no one is mouthing the words, or is in sync with those words. Even if the yelling came from offscreen (i.e. from the farthest bleachers) the noise should have sounded from far away, not as neat and close as it sounds.
Revealing mistake: In some of the scenes where we see Maggie in the hospital bed, you can see that her breathing is not totally in sync with the breathing machine (i.e. her chest goes up before you actually hear the machine blowing air into her).
Factual error: It is said Maggie can't breathe on her own after her injury. If this was the case she wouldn't be able to speak, since she can't push air out of her lungs to generate sound.
Factual error: Hilary Swank is driving to the new home she bought for her mother, which is supposed to be in Missouri. Why do we see palm trees on the side of the road?
Answer: No, the cause of conflict between Frankie and his daughter is never revealed - we only know that she returns his weekly letters, and it has been some time since they have had contact.