Perhaps Naruto has started to see Sakura's hitting as disrespectful. In the story, he could be on a journey of self - discovery and realizing his own worth, so he doesn't allow her to physically assault him as she used to. He might be thinking that he deserves to be treated better.
One possible reason could be that Naruto has grown tired of Sakura's violent tendencies towards him. He might have reached a point where he decides to stand up for himself and not tolerate being hit any longer.
It could also be that Naruto has some newfound confidence or a different relationship dynamic with Sakura in this fanfic. Maybe he has developed feelings for her in a new way and doesn't want her to hit him because it goes against the more tender feelings he now has. Or maybe he has made a promise to himself to be more assertive in all his relationships, and this is just one aspect of that.
She might be shocked at first. Sakura is used to Naruto being more passive when it comes to her hitting him, so when he suddenly stops her, it could catch her off - guard.
One possible reason could be a clash of personalities. For example, if Naruto is too impulsive and his team members are more cautious, it can lead to friction. Maybe in the fanfic, Naruto's unwavering belief in his own way of doing things doesn't align with the more strategic or traditional approaches of his teammates. This could cause misunderstandings and make it seem like they don't work well together.
Another reason could be that Naruto is trying to protect Sakura in his own way. He might think that by ignoring her, he can keep her out of harm's way. If he senses that there are dangerous enemies lurking around, he could be trying to create a distance between them so that Sakura doesn't get caught up in any potential battles or threats.
Well, in the fanfiction context, Naruto may not love Sakura because he has unrequited feelings for someone else. Maybe he has a deep connection with another character that makes him view Sakura just as a teammate. Also, their personalities might not be as compatible in a romantic sense as one would initially think. Naruto is often impulsive and headstrong, while Sakura can be a bit more reserved in some ways, and this could lead to a lack of romantic attraction.
One possible reason could be that something happened during the Kage Summit that made Naruto lose trust in Sakura. Maybe she made a decision or took an action that he didn't agree with. For example, if she sided with someone against Naruto's ideas regarding the situation at the Summit.
It could also be due to Sakura constantly doubting Naruto's abilities in the story. Naruto has always been looked down upon by many in the original series, and if in the fanfiction Sakura continuously expresses her lack of faith in him, it could lead to his unforgiveness. For example, she might have refused to believe in Naruto's new jutsu or his plans to save the village, which made Naruto feel really disappointed and unable to forgive her.
It could be that Sakura has done something that has disappointed Naruto deeply. This could range from her making a decision in a mission that Naruto didn't agree with, to her not being there for him during a difficult time. These actions might have gradually eroded his love for her.
One possible reason could be that he has seen the darker side of the ninja world. Maybe he witnessed too much death and destruction during his missions and decided he no longer wanted to be part of it. Another reason might be that he has other dreams that he realizes are more important to him than being a ninja. For example, he could have a passion for art or music that he wants to pursue instead.
One possible reason could be that he has some crucial information that Sakura needs. Maybe he knows secrets about their world or a powerful enemy, and if he escapes, that knowledge will be lost.
One possible reason could be Naruto's over - eagerness to prove himself. Naruto is always trying to show that he's strong and capable, and sometimes this might come across as him not considering Sakura's feelings or opinions. For example, he might rush into a dangerous situation without consulting her, which could lead to an argument as Sakura is also a capable ninja who wants to be part of the decision - making process.