Continuity mistake: In the dance contest, Pat's shirt is tucked in at the beginning. During the "Fell In Love With a Girl" portion his shirt comes totally out. Subsequently his shirt is tucked in again.
Continuity mistake: Bradley Cooper wears a necklace. While rehearsing a dance sequence with Jennifer Lawrence the necklace is alternately hanging on his chest then back, indiscriminately between cuts.
Continuity mistake: In a scene in the dance studio, Pat enters and you can see that his tennis shoes have duct tape on them. In the next shot, Tiffany is bending over, taping the same shoes that don't yet have tape on them.
Continuity mistake: When Danny is speaking with Dolores about the food she is preparing, in the first shot his lips are moving as he's speaking to her but in the second shot a moment later, they are not. (01:50:55)
Continuity mistake: When Pat first gets home near the beginning and is having a conversation with his parents in the hall, his father pulls out his neck chain to check he still has it, then in the subsequent shots it switches between in and out several times.
Continuity mistake: When Bradley and Jennifer arrive at the dance competition they end up holding hands. As they make their way upstairs to register, Bradley is on the left of the picture, but as the scene cuts (in real time) from them starting up the stairs to getting to the top, they have switched sides. Then, very briefly, when Jennifer goes to use the restroom, they have switched back again.
Continuity mistake: At the end of the dance competition Tiffany leaves the ball room, putting her coat on over her white outfit. She then runs through the Hotel foyer and out into the street. When she gets outside she is wearing black tights under her coat.
Continuity mistake: In a group scene with Bradley Cooper's family, Jennifer Lawrence arrives and has a beer. While she's talking the camera pans the group. At one point Bradley Cooper responds. While the camera is still on Lawrence, you can see Cooper at the left of the screen. Although talking, his jaw isn't moving.
Continuity mistake: When Pat starts to read the letter from Nikki, the golden jewel is outside of his shirt, then suddenly inside. (01:19:30)
Continuity mistake: Deniro starts taking off his jacket at the dance competition and it's halfway off his left shoulder. In the next shot his jacket is back on.
Continuity mistake: When Tiffany meets up with the family at his home and they're discussing football, she's drinking a Bud, then after an angle change she is standing with her arms folded.
Continuity mistake: When Veronica takes Pat and Tiffany on a tour of her house, she bends down to light her fireplace and on the left you can see an iPod in the wall-mounted iPod dock. A little after this, she shows them the dock, and it is empty again.
Continuity mistake: In the scene where Tiffany is attempting to put a full length tie on Pat for the dance competition, Pat's collar is up and down inconsistently.
Continuity mistake: At the end of the dance competition, Pat hugs Tiffany and starts walking towards Nikki. After he reaches where she is standing in the close-up shot, the subsequent distant shot which follows shows him still approaching her.
Answer: It's not exactly common, but yes, it would be up to the judge, and establishing that a person is a "clear and present danger to themselves or others" can result in involuntary commitment in Pennsylvania, where the film takes place. In this case, it would not be hard to argue that, "the person has inflicted or attempted to inflict serious bodily harm on another and that there is a reasonable probability that such conduct will be repeated" (50 PA. CONS. STAT. ANN. ยง 7301 (b) (1)), as he had just physically assaulted his wife's lover and she'd obtained a restraining order. His mental health problems would have been well-documented, so it would have been easy for a judge to order him to undergo psychiatric evaluation, which could (and, in the film, does) lead to extended involuntary commitment at the discretion of a mental health professional.