It could also be a matter of desperation. Perhaps there is a threat to the village or someone she loves dearly, and she believes that Naruto holds the key to solving the problem. But instead of asking him directly, she kidnaps him in a hasty and ill - conceived plan. This could lead to a lot of drama and character development as Naruto tries to understand her actions and they both work towards resolving the real issue.
It could be that Naruto has lost his sanity temporarily. The stress of being a hero, the constant battles, and the losses he has endured might have taken a toll on his mental state. In this state of instability, he may see Sakura as a symbol of something he wants to preserve or protect, but his way of doing so is through kidnapping. Or there could be a new villain in the story who has the ability to make Naruto act out of character, and this villain's plan involves Naruto kidnapping Sakura.
One possible motive could be to force Naruto to understand his own power. Sasuke might think that by kidnapping Naruto, he can push Naruto to a situation where he has to tap into his full potential. Maybe Sasuke feels that Naruto has been relying too much on his friends and needs this shock to grow stronger on his own.
One possible motive could be jealousy. Maybe Naruto has achieved something that Sakura desires, like getting more recognition in the village. So, she decides to frame him to bring him down a notch.
One possible motive could be mind control. Maybe an enemy uses some kind of jutsu to make Naruto lose control and attack Sakura. Another could be a misunderstanding. For example, if Sakura was framed for something really bad, and Naruto in his hot - headedness believes it and attacks her. Or perhaps in a dark, alternate universe version of the Naruto world where the characters' personalities are twisted, Naruto might have a reason to attack her based on that altered personality.
One possible motive could be that in the fanfiction, Adrien is being controlled by some dark magic or an evil force. This external influence makes him act against his true nature and kidnap Marinette. For example, perhaps a villain has cast a spell on him to use him as a tool to get to Marinette, who might have some special power or knowledge that the villain desires.
Maybe she's trying to protect Naruto from something she knows about but others don't. She might think that by kidnapping him, she can keep him safe from an imminent threat that the village or his friends are unaware of.
Well, in some fanfiction, it could be a plot device to create a huge rift in the relationship between Sakura and other characters. If Sakura stabs Naruto, it would shock everyone. Maybe she was influenced by a dark power or an ancient curse that made her turn on Naruto. This would lead to a complex web of events where characters have to deal with the aftermath, both in terms of their emotions and the overall balance in the ninja world.
It could also be for revenge. Perhaps Stiles or someone associated with him has wronged Peter in the past within the context of the fanfiction story. So, Peter kidnaps Stiles to get back at him or those related to him. Another reason might be that Peter is being controlled by some other force. There could be a dark entity manipulating Peter's actions, and it makes him kidnap Stiles for its own sinister purposes.
One possible motive could be Damon's possessiveness. In the 'The Vampire Diaries' universe, Damon has a complex relationship with Elena. He might kidnap her out of fear of losing her to someone else, like Stefan. Maybe he thinks that by taking her away, he can have her all to himself and make her see that he is the one she should be with.
One possible motive could be related to power. Maybe Sasuke thinks that Hinata has some sort of connection or knowledge that could help him gain more power. For example, her Byakugan might be of interest to him in terms of seeing things that he couldn't otherwise. Another motive could be a misdirected sense of revenge. He might believe that Hinata is somehow connected to someone he wants to get back at. It could also be a plot by an outside force that is controlling Sasuke to kidnap Hinata, perhaps for some kind of experiment due to her unique abilities.