Sasuke could be one. Given their complex relationship, there could be a situation where Sasuke's newfound power or different ideology leads him to fight and beat Naruto in a fan - made story.
Well, in a lot of these fanfictions, Stiles can get beat up due to his own recklessness. He might be so determined to solve a mystery or help his friends that he doesn't think about the consequences and ends up in a dangerous situation where he is outnumbered and beaten up. Also, there could be miscommunication. Maybe someone thinks he has done something wrong when he actually hasn't, and they take matters into their own hands and beat him up.
In my opinion, it's highly unlikely. Goku has mastered multiple forms and techniques that give him a wide range of powers. Saitama's one-punch style might not be effective against Goku's diverse skills and battle experience.
Maybe some new kids in the neighborhood who are trying to establish their dominance and pick on Lincoln as an easy target. They might not know much about him or his family, but just see him as someone they can bully.
It could be an antagonist character in the Septiplier fanfiction world. Maybe someone who has a grudge against Jack for some reason, like a rival in a game or a love interest situation gone sour.
I don't think there's a clear winner. Both Manga Goku and Manga Saitama have unique and powerful abilities. It could come down to strategy, luck, or even the author's imagination!
In some fanfictions, Naruto might get beat up when facing a powerful new villain who has some unknown jutsu. This could be a villain created by the fanfic writer to test Naruto's limits.
Well, in a 'jack gets beat up septiplier fanfiction', it could be that the writer is exploring a darker side of the relationship dynamics within the Septiplier fandom. It could be that Jack has made an enemy within the story's context, perhaps someone jealous of his relationship with another character. The beat - up could be a way to create drama and tension in the fan - created narrative.
One possible reason could be that he's gotten on the wrong side of a powerful client. Maybe he uncovered some shady business deals of the client during a case, and the client decided to take revenge by having him beaten up. Another reason might be related to his past. If some of his old associates from his pre - Harvey days found out he was now working in a high - profile law firm, they could be jealous and target him.
Well, perhaps Johnny made some mistake that angered Jally's group. Maybe he accidentally insulted Jally or got in the way of something Jally cared about. So Jally, with his friends, decided to teach Johnny a lesson by beating him up.