One possible reason could be a misunderstanding. Maybe Sakura misinterprets Naruto's actions or words, thinking he has betrayed her or their friends in some way, which leads to her hurting him one last time in a fit of anger.
On the other hand, Naruto could also be understanding. If he realizes that Sakura has her reasons, even if they are wrong, he might try to forgive her. Naruto has always been one to see the good in people, and he might hope that they can work through whatever has caused this situation. He may try to talk to her calmly to resolve the issue, showing his maturity and his belief in their friendship.
One reason could be to add drama. By having Naruto hurt Sakura, it creates conflict which is a key element in storytelling. It can make the plot more interesting and engaging as it forces other characters to react and deal with the situation.
Sometimes, in fanfiction, Sakura might use her medical skills against Naruto in a negative way. For example, if she withholds treatment or gives him a wrong diagnosis out of some conflicted feelings towards him. This is quite cruel and can cause both physical and emotional harm to Naruto.
There are also fanfictions where Sakura's actions in choosing Sasuke over Naruto in a more hurtful way than in the original series can be explored. She might publicly reject Naruto in a cruel manner, causing him to question his self - worth. Naruto then might go on a journey of self - discovery to prove himself not just to Sakura, but to the whole village.
Naruto might initially be shocked and heartbroken. He may try to hide his pain and put on a brave face, as he has always done in the face of adversity. He could also become withdrawn for a while, distancing himself from Sakura as a form of self - protection.
It can change the perception a lot. Fans who read such fanfiction might start to view Sakura in a more negative light, even if in the original she had her redeeming qualities. For example, if in the fanfiction she is constantly mean to Naruto, it can overshadow the times she was actually a good friend to him in the original story.
One common scenario is when Sakura chooses Sasuke over Naruto time and time again. It makes Naruto feel like he's second best, which deeply wounds his heart as he loves her so much.
You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). These platforms have a large collection of Naruto - related fanfictions, and there's a good chance you'll find 'itachi hurts sakura fanfiction' among them.
In some 'itachi hurts sakura fanfiction', it might involve a misunderstanding. For instance, Itachi thinks Sakura is a threat to Konoha's secrets and has to take action against her. However, as the story progresses, he realizes his mistake. It could also be a story set in an alternate universe where the power dynamics are different and Itachi's actions towards Sakura are a result of that different setup.