Well, it could be that Harry, at that moment, saw Draco not as his rival but as a fellow student. In the wizarding world, Quidditch can be a very dangerous sport. Harry might have thought about how his friends would feel if he were in Draco's position. Also, Harry has a heroic streak. He might have instinctively jumped into action without really thinking about who it was he was saving. His first impulse could have been just to stop a potential disaster from happening on the pitch.
In some fanfictions, it could be a result of some magical influence. Maybe there was a spell or a charm that made Harry act this way. Or it could be an expression of deep - seated emotions that Harry has been suppressing for a long time. This action then becomes a way for him to break free from his self - imposed restraints and reach out to Draco in a very physical way.
Well, Harry might save Daphne from Draco because Harry is always the hero type. He doesn't like Draco's pure - blood supremacist attitude. Daphne could be a target of Draco's cruel remarks or actions just because she might not fully conform to Draco's ideas. Harry, being the defender of the underdog in many cases, steps in. Also, it could be that the plot of the fanfiction is building a new alliance or relationship web, and Harry saving Daphne is a key part of that, leading to new story developments.
One possible reason could be that in the fanfiction, the wizarding community in England has turned against Harry due to some false accusations. Maybe a powerful dark wizard has framed him for a series of heinous crimes, and the public, being misled, forces him to leave. Another reason might be political intrigue within the Ministry of Magic. There could be a new regime that sees Harry as a threat to their power and thus kicks him out.
Perhaps there is some external threat or danger related to Quidditch. Maybe there is a dark wizard who is targeting Quidditch players and Harry doesn't want to put himself or his friends in danger. He has already faced so many threats in his life that this additional risk related to Quidditch might be too much for him.
Perhaps Draco has developed a sense of respect for Harry over time. He might have seen Harry's courage and determination up close and decided that Harry is worthy of his help. Throwing the wand could be his way of showing that he acknowledges Harry's importance in the fight against the common enemy.
In the fanfic, perhaps Harry had reached his limit with Umbridge's blatant disregard for the rights and well - being of the students and magical creatures. She was a symbol of the corrupt Ministry at that time. Harry, having a strong sense of justice, could no longer tolerate her presence and actions, especially after seeing how she treated his friends and those he cared about at Hogwarts.
One possible plotline could be that Voldemort realizes that Harry is the key to some greater power or knowledge that he wants to obtain. So, instead of killing Harry, he saves him from another dark wizard or a dangerous magical creature. Maybe he sees that Harry has a connection to an ancient magic that could help him rule the wizarding world in a more complete way.
Another reason could be a build - up of years of pent - up anger and frustration. Snape has been harsh on Harry throughout his years at Hogwarts. Harry has had to endure Snape's unfair treatment, and all of that negative emotion could explode in a moment of extreme stress or danger, leading him to stab Snape.
Perhaps the author is trying to be different. Since so many fanfics already focus on Harry and Quidditch, they choose not to.
Maybe Draco says some really mean and hurtful words to Harry. For example, he might make fun of Harry's family situation, like his parents' death or his relationship with the Dursleys. Words like that can be really cutting and could easily make Harry cry.