One possible plotline could be that Sasuke is under some sort of dark magic or mind control when he binds Sakura with snakes. Maybe an enemy has manipulated him into doing this as part of a larger scheme against the Hidden Leaf Village. And Sakura, being the strong - willed kunoichi she is, tries to break free and also reach out to the real Sasuke within his mind - controlled state.
It could be that Sasuke binds Sakura with snakes in a moment of extreme anger or misunderstanding. He thinks Sakura has done something to endanger his goals or the safety of someone he cares about. However, as the story progresses, he realizes his mistake and has to find a way to make amends while Sakura has to decide whether to forgive him or not.
Perhaps in the fanfiction, the snakes are not ordinary snakes but have some special abilities. Sasuke uses them to bind Sakura as a way to keep her from interfering in a dangerous mission he has to undertake alone. But Sakura sees it as a betrayal and fights back both physically and emotionally, leading to a complex relationship dynamic between them throughout the story.