Continuity mistake: In the scene where Viola meets up with Justin at the carnival, in one shot Justin's right collar is flapped down, in the next shot it is up.
Continuity mistake: When Sebastian (really Viola) is trying to impress the guys at Cesario's, she uses her friends as the plan. When her second friend, Yvonne, comes over and starts to walk towards Sebastian (Viola),right before she hugs him, she is really close, but when she actually hugs him she is further back then before.
Continuity mistake: In the carnival fight scene, right after Justin throws a cheap shot at Duke, they fight and fall off the stage. Justin's boxers are black. As they continue fighting, you can see multiple times that Justin's character is now wearing white boxers. The black boxers were his stuntman's. (Confirmed on DVD special features).
Continuity mistake: In the scene where Viola is in the principal's office she retracts her hand twice when he says not to touch the plaque.
Continuity mistake: When Viola is talking to her mother at the carnival she says completely 'okay, have a good carnival' before turns away. In the next shot, you can see her still saying 'val'.
Audio problem: In the scene where the guys are looking at Olivia, talking about her nodding at Sebastian, Sebastian says something, then his phone rings. He continues mouthing something over the ringtone, but no sound is heard.
Continuity mistake: When Viola reveals that she is a girl she takes her wig of and her real hair is a mess. The camera changes shot to look at Duke but when it goes back to Viola her hair looks normal like it has been brushed.
Audio problem: In the fight scene, in the bathroom, right as Viola jumps on Monique's back, Monique says "Get off me", the camera is looking right at her, but her mouth doesn't move when she says it for the first time.
Continuity mistake: At the final kiss scene between Viola and Duke and the end of the movie, they walk towards each other and begin kissing with their hands at their sides. In the next shot, Duke's hand is now on Viola's face, with no time to move it between shots.
Continuity mistake: In the scene with Olivia and Viola; after Olivia asks Duke out and they walk out side to the bleachers, when they sit down the shadow behind them is different from when they stand up.
Continuity mistake: At the soccer game when Viola removes her wig and she fluffs out her hair, in one shot the wig is in her hand and the next it's gone.
Continuity mistake: In the scene where Viola is telling her mom she will be staying with her dad for two weeks, her shirt changes. When she's facing away, you can see the white tank under the blue shirt, but when she turns and walks into the dining room to talk to her mom, you can't see the white shirt. When she hugs her mom and leaves the house, the white tank is visible again. She doesn't adjust it in the scene.
Plot hole: Viola convinces her mother she is staying at her father's house for two weeks, but who covers for Viola with school administrators? As far as we see in the movie, Viola is not reported absent from either Cornwall or Illyria (a transfer would explain not being reported absent from Cornwall). Administrators or class mates at Cornwall would find it strange that she stopped showing up, since soccer training had already started. It is unlikely Viola officially transferred to Illyria, since her parents would have to sign off on that, or at least start paying her tuition to a different school. Viola could have called in sick to either Cornwall or Illyria, but this is never addressed in the movie. And if the soccer program at either school started before the official school year, it would make no sense for them to have a biology class with students not enrolled in athletic programs at Illyria.
Factual error: A soccer game does not end on a goal. The ball is always returned to the middle of the pitch for a kick-off, after which the game is ended by the referee. It is also highly unlikely no overtime is given in this game, seeing the number of interruptions.
Continuity mistake: In the scene at the beginning when Viola is walking up to her house and Monique stops her, when she turns around you can see the tip of her ear through her hair and then when it comes back you can't. It changes throughout the scene.
Continuity mistake: At the carnival, when Duke and Justin get into a fight and Viola jumps on them, the three of them fall into a popcorn machine. Viola's mother then comes running through the crowd to see what the commotion is. There is a shot from behind her shoulder of her pushing through the crowd into the clearing, then the next shot is of her from the front, where she is pushing through that crowd into the clearing again. The people in the crowd also change.
Continuity mistake: When Viola is changing into her boy clothes when she's on the carnival ride, she puts her clothes on over her dress, but when she changes back into her girl clothes she takes her dress out of her bag to put it on.
Continuity mistake: Right before the game between Cornwall and Illyria, Duke and Justin are facing off and flipping the coin. In the far shot Justin only has his left glove on. But when the camera comes in close and Justin punches his chin, he has two gloves on. He doesn't put it on in the scene.
Visible crew/equipment: Right after Viola is done talking to her brother and he goes out the window, her mom walks into the room and then it pans back to Viola and right above her is part of the boom mic, then it goes back to her mom, and then when it goes back to Viola for the final time you can see the boom mic now right above her head.