One possible reason could be misrepresentation of her character. In some fanfictions, authors might change her personality to fit a certain plot, like making her overly jealous or mean, which would be out of character for the gentle Hinata. This could make her seem unlikable and thus anger fans who love the original Hinata.
It could also be due to the power levels or skills attributed to her in fanfiction. If she is made too weak or too powerful in a way that doesn't align with the original Naruto universe's logic, it can be off - putting. For example, if she suddenly has powers that make no sense in the context of the chakra system in Naruto, it can anger fans who appreciate the consistency of the world - building in the original series.
It could also be due to jealousy. If Naruto is spending a lot of time with other female characters, Hinata might get angry. Even though she is usually shy and reserved, her love for Naruto could turn into anger if she feels threatened by his closeness to others.
One reason could be Boruto's recklessness. In fanfiction, Boruto might engage in dangerous stunts or actions that go against Naruto's teachings. For example, if Boruto were to use a forbidden jutsu without fully understanding the consequences, Naruto would be angry as it not only endangers Boruto but also those around him.
One possible reason could be that Tsunade makes a decision regarding the village that Naruto strongly disagrees with. For example, if she refuses to send help to a neighboring village in need, Naruto, with his strong sense of justice, might get angry. He's always been about protecting and helping others.
Another reason could be in a fan - created scenario where there are secrets involved. Hinata might be keeping a secret from Naruto that, when revealed, makes Naruto feel betrayed or deceived. This sense of betrayal could easily turn into anger. For instance, if Hinata has a connection to an enemy that she's been hiding from Naruto.
Maybe the fanfiction portrays Hinata in a way that doesn't align with her true character. For example, it might make her overly aggressive or weak in a way that doesn't fit the original concept.
It could be due to external pressures. Maybe the village has certain expectations of them as a couple that they can't meet. Or there could be a threat to the family that Naruto, in his role as a protector, doesn't handle well, making Hinata lose faith in their relationship.
Maybe she wants to keep her real relationship with Naruto pure. Fanfiction can be full of all sorts of wild and untrue interpretations of their relationship. She values what she has with Naruto in reality and doesn't want to be influenced by fictional ideas. For example, some fanfictions might create unnecessary drama or unrealistic scenarios between them.
One event could be if Hinata is forced by her family to make a decision that goes against Naruto's wishes. For example, if her family arranges a marriage for her with someone else, Naruto might be angry at her for not standing up to them. He values freedom and choice, and if he thinks Hinata is giving in too easily, it could make him angry.
In the fanfiction, it could be that Kakashi is being too hard on Naruto during training. He might be pushing him beyond his limits without proper explanation or support, causing Naruto to feel frustrated and angry. Naruto is a determined character, but everyone has their breaking point.
One possible reason could be a huge misunderstanding. Maybe he thought Hinata did something really bad to his friends, like unknowingly leading the enemy to them. Without knowing the truth, his hot - headed nature made him lash out.