It's the end of the film...the big title fight in London. Welterweight "Irish" Micky Ward waits in the wings with his older half-brother and trainer, Dick "Dicky" Ecklund, who has only recently kicked a nasty crack cocaine habit.
It's a loaded moment. So much struggle has gone into it, on both sides. Micky has had to work like a fiend to regain his boxing career. Dicky's fight has been to break his addiction and win back his brother's trust.
The brothers bow their heads toward one another, touch foreheads. Micky's entrance music starts to play, "Here I Go Again," by Whitesnake. Dicky starts to sing it softly.
Here I go again on my own
Going down the only road I've ever known
Like a drifter, I was born to walk alone
And I've made up my mind
I ain't wasting no more time
Earlier in the film, there's a scene in which Dicky's mom catches him in a crack den and in the middle of the ensuing argument, Dicky starts singing the Bee Gee's "I Started a Joke" to her. It's clear he knows it's her favorite and sure enough, she joins in despite herself. This scene shows Dicky still has charisma to burn despite years of dissapation and that he uses it both to soothe and manipulate those around him. Later, when he gets sober, Dicky's force of personality becomes that much more dazzling. We watch him rescue lost confidences and form seemingly impossible alliances.
Back in the hallway before the fight, Micky joins him in singing. The rest of the world falls away and the brothers are together again, ready for the fight. They step out into the crowd together and make their way toward the ring.
At this point, most directors would have transitioned to just the Whitesnake, mixing the bombast of the hair metal with the din of the crowd. Instead, David O. Russell lets us hear that the brothers are still quietly singing together, for the entire duration of their walk up to the ring. The intimacy and unexpectedness of that private duet is what makes it so moving. This is song as ritual and shield. We feel the fierceness of the brotherly love and understand the victory this walk represents for each of them, before the first bell rings.