Robert De Niro (Pat, Sr.) teared up during the scene when he tells Bradley Cooper (Pat, Jr.) he wished he was closer to him, which was not scripted.
Bradley Cooper and Jennifer Lawrence spent several weeks practicing the climactic ballroom dance routine with choreographer Mandy Moore. "None of that was improvised, absolutely not," asserts Lawrence. "I'm a terrible dancer, so I would never have been able to do any of that. When it finally came together, that scene really was just as fun as it feels." Lawrence even mentioned that compared to her, Cooper took to dancing quite naturally, when in fact, it's her character Tiffany that's supposed to be the experienced dancer, and Pat, the amateur.
David O. Russell has said in interviews that one of the main reasons why he cast Bradley Cooper was that, seeing his work, he noticed that sometimes Cooper looked really angry and tried to suppress it, something he needed for the character of Pat.
It took five years and twenty-five re-writes before David O. Russell could direct it, as Sydney Pollack told him it was tricky to have emotional, troubling, funny, and romantic content mixed together.
David O. Russell was drawn to the story because of the family relationships, and also because of the connection to his own son Matthew Antonio Grillo Russell, who has bipolar and O.C.D.