One possible reason could be a simple rivalry that has boiled over. Maybe they were competing for the same mission, and Naruto's determination to prove himself got the better of him. He might have seen Kiba as a threat to his goal of becoming Hokage, thinking that if Kiba succeeds in a high - profile mission, it could overshadow his own achievements.
It could also be due to a misunderstanding. Perhaps Kiba said something that Naruto misinterpreted as an insult to his friends or his village. Naruto is very protective, and he wouldn't stand for any slander against those he cares about. So, in a fit of anger, he lashes out at Kiba.
Another aspect could be related to their different ninja styles. Naruto's more brash and go - for - it style might clash with Kiba's more animal - based and instinctive style. During a training session or a spar, their differences could lead to a more intense fight where Naruto ends up beating Kiba. This could also be a way for Naruto to show that his style is just as effective, if not more so, than Kiba's.
One possible reason could be a misunderstanding. Maybe Sakura makes a decision that Naruto strongly disagrees with regarding the safety of the village or their friends. For example, if Sakura decides to trust an enemy without Naruto's knowledge, Naruto might get so angry that he lashes out at her.
Maybe Sakura gets angry at Naruto for some misunderstanding, like he accidentally ruins one of her important medical experiments. So she decides to beat him up to teach him a lesson.
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.
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.
A misunderstanding is also likely. Maybe Kiba overhears a conversation that he misinterprets. For instance, he might think Hinata is talking badly about him when in fact she is just discussing a general ninja problem. This could make him angry enough to hurt her, either with words or actions.
One possible reason could be a misunderstanding during a battle. Maybe there was some sort of jutsu misfire or misinterpretation of an attack. For example, if Kiba was using a new and powerful technique that Naruto didn't recognize, Naruto might instinctively go all - out in self - defense, nearly killing Kiba.
It could also be that Naruto has unspoken feelings for Hinata. So when Kiba steals from her, it's not just about the act of stealing, but also a sort of territorial thing. He feels the need to defend her honor, like a knight in shining armor.
One possible reason could be envy. Flash might be jealous of Peter's intelligence or popularity at school. Maybe he feels overshadowed by Peter and his achievements, so in the fanfiction, his anger and frustration lead him to lash out physically.
Perhaps it could be about a competition between Naruto and Kiba during a particularly intense training session. They both get really 'in the zone' or 'in heat' in terms of their competitive spirit. Naruto might be using his new jutsu while Kiba is pushing Akamaru to their limits. This could lead to some friendly rivalry and growth for both of them.
In this fanfiction, perhaps there is a misunderstanding between Luke and Percy. Luke might think Percy has betrayed him in some way, like siding with the wrong people in the context of their fictional world, and thus resorts to violence by beating him up.