Hinata might be shocked at first. She is a gentle soul, so seeing Naruto be so violent towards Sasuke would be unexpected. But then she would probably try to stop Naruto, as she doesn't like to see people fighting. She might also feel a bit guilty, thinking that her relationship with Naruto somehow caused this conflict between the two friends.
Well, in such a fanfiction, perhaps Sasuke has some sort of plan that involves Hinata in a negative way. Naruto discovers this and decides to beat up Sasuke to protect Hinata. It could also be part of a bigger struggle where Sasuke's actions are seen as a threat to the future Naruto envisions with Hinata, so Naruto takes matters into his own hands to stop him.
Sasuke would likely be very conflicted. On one hand, he has his own relationship with Naruto and Sakura. He might initially be angry at Naruto for attacking Sakura. But if he discovers the reasons behind it, he may understand Naruto's actions to some extent.
Shikamaru would likely be lazy about getting involved at first. But if it started to cause a big ruckus in the village or among their group of friends, he'd step in. He'd probably analyze the situation quickly and try to find a logical solution. He might tell Naruto to cool off and Kiba to stop provoking Naruto if that was the case.
Hinata would be heartbroken at first. Naruto is someone she deeply cares about. But she's also a strong - willed ninja. So she might start by trying to understand why Naruto left. She could look for clues in the village or talk to Naruto's friends to figure out his possible destination.
Hinata would likely go to great lengths to save Naruto. She might seek help from the most powerful medical ninjas in the village or even venture out to find a rare herb or a mysterious healer. She would be in a state of shock at first, but then her love for Naruto would drive her to take action.
In some fanfictions, Naruto is completely oblivious at first. He doesn't understand why Hinata is acting strange. He just goes about his day, being friendly as usual. But as Hinata's jealousy becomes more obvious, he might start to notice that something is wrong. He could be confused and try to ask Hinata what's bothering her.
Hinata might be initially worried. She doesn't want any conflict between Naruto and Sasuke because she cares about both of them. But at the same time, she could feel a bit flattered that Naruto is so protective of her.
Hinata might be shocked at first. She has always adored Naruto, and this sudden act of aggression from him would leave her stunned and unable to process it immediately.
On the other hand, there would be fans who would welcome it. Maybe they never liked the pairing in the first place or they think it adds an interesting twist to the story. They could start exploring new relationships for both Sasuke and Sakura in their own fan - created stories.
At first, Naruto would be completely shocked. He has always seen Hinata as a loyal friend and someone who has deep feelings for him. So the idea of her betrayal would be hard to fathom. He might try to deny it at first.