It might signify a shift in their relationship dynamic. Maybe the writer is exploring a new, unexpected connection between them.
The struggle could be a symbol of Sakura's inner turmoil. She could be torn between her loyalty to her friends or village and this new, strange situation with Itachi.
It may also be used to create tension and intrigue in the fanfiction. It makes the reader wonder what led to this situation and what will happen next.
In this kind of fanfiction scenario, it could be due to various reasons. Maybe Sakura is in a state of shock or confusion. Itachi is often depicted as a very complex and somewhat intimidating character in the Naruto universe. Sakura might be frozen in place because she's not sure how to react to being so close to him. It could also be that there are some external factors, like a jutsu that has immobilized her or some kind of emotional turmoil within her that's preventing her from simply getting up and leaving his lap.
One possibility is that Sakura tries to communicate with Itachi. She might try to reason with him, asking him why he has her captive. This could lead to some revelations about Itachi's true intentions. If Itachi is part of some bigger plot, Sakura could find out crucial information during this conversation, which could either make her situation worse or give her a chance to escape.
It could also be related to protecting her. In the Naruto universe, there are many powerful and dangerous forces. Itachi might see that Sakura is in over her head in a situation and by immobilizing her, he's ensuring her safety until he can figure out how to deal with the threat. For example, if she's about to engage with a foe far stronger than her, he steps in to stop her.
One reason could be that he sees something special in Sakura. Maybe he admires her strength or her kind heart, and he doesn't want to lose her to someone else who might not appreciate her as much as he does.
It can be a turning point in the story. If the fanfiction was previously focused on Sakura's independent actions, this immobilization can change the direction completely. She might have to rely on others or use her wits in a different way to get out of this situation. Itachi's actions here can also introduce new plot elements, such as secrets he reveals while holding her or new alliances that form as a result of this encounter.
Well, perhaps the plot could involve Sakura being assigned as Itachi's secretary in a powerful ninja organization. At first, Itachi is cold and distant towards her, but Sakura is determined to do her job well. As time passes, they start to have mutual respect for each other's skills. Then, an external threat to the organization emerges, and Sakura and Itachi have to work together closely, which leads to a deeper understanding and maybe even the start of a romantic relationship between them.
Perhaps in the fanfiction, Sakura and Itachi are in a police force that has to deal with international ninja disputes. Sakura, with her intelligence and strong will, and Itachi, with his strategic mind, work together to prevent a full - scale war between two large ninja clans. They face many challenges along the way, including distrust from their own comrades who are skeptical of their unorthodox methods.
The plot could involve Itachi noticing Sakura's isolation within her own team at some point. He decides to adopt her in a sense, like becoming a mentor to her. Itachi could share his insights on how to deal with powerful enemies and the sacrifices one has to make for the greater good. Sakura would then grow not only in her combat skills but also in her understanding of the complex world of ninjas. She might start to see things from a different perspective, similar to Itachi's, which could cause some friction and also growth within her relationships with Naruto and Sasuke.
It could be a story where Itachi has some sort of ulterior motive for restraining Sakura. Maybe he's trying to protect her in a very unorthodox way. For example, he might be aware of a danger that only he can sense, and by restraining her wrists, he's ensuring she doesn't run into harm's way.
One possible plot could be that Sakura, with her new family connection to Itachi, gets trained by him in secret. This would make her much more powerful and give her an edge in the ninja world. It could also lead to her being targeted by the same enemies as Itachi.