In the fanfic, Harry could be alerted to the situation by his magical intuition. He arrives just in time to see Ron raise his wand at Hermione. Harry, having practiced his dueling skills, quickly deflects Ron's spell and counter - attacks with a binding spell. He then pulls Hermione away from the scene. As they flee, Harry tells Hermione that they need to find a way to remove the negative energy that has seemingly taken over Ron. They might decide to go to the library to research on ancient spells that could help in such a situation.
Maybe Lucius wants to gain an advantage. He could see Hermione as a powerful witch with knowledge that he can use for his own ends. By saving her from Ron's beaten, he hopes to earn her gratitude and get access to her skills or information.
Maybe Harry uses his magic skills to immobilize Ron. He could cast a spell like 'Petrificus Totalus' on Ron right when he's about to attack Hermione, thus stopping the beating.
In my version of the fanfic, Harry was in the Gryffindor common room when he noticed Ron's strange behavior towards Hermione. Ron seemed to be in a trance and was about to lash out at Hermione. Without hesitation, Harry jumps in front of Hermione and uses a Patronus charm to repel Ron. The Patronus, in the form of a stag, charges at Ron and knocks him back. Harry then holds Hermione's hand and leads her through the secret passages of Hogwarts. As they run, Harry tells Hermione that they need to find a way to break whatever spell or curse is on Ron. They end up in Dumbledore's old office, where they start to search for answers in the old books and magical artifacts left behind.
Well, he could use his magic skills. Maybe he casts a powerful spell on Ron to stop him and then takes Hermione to a safe place, like Hogwarts where there are protective enchantments.
One possible plot could be that in a dark and alternate version of the wizarding world, Ron has been influenced by some dark magic or a powerful enemy who has turned him against Hermione. Lucius, for his own reasons (maybe to redeem himself or because he sees the value in Hermione), steps in to save her. He might use his powerful family connections and knowledge of dark magic to counter whatever threat Ron poses.
Well, it could be related to Ron's insecurities. He might be insecure about his place in the group with Harry and Hermione. Hermione is always so confident and sure of herself, and Ron might feel that he doesn't measure up. This could translate into aggression as a way of lashing out. Also, perhaps there's some external influence, like a dark magic object that's affecting Ron's mood and behavior towards Hermione.
Well, in some versions, Ron might use his quick wit and knowledge of Hogwarts' secret passages to outmaneuver Draco. He could lead Hermione to safety through a passage that Draco doesn't know about.
Maybe a new dark wizard or witch emerges. This character is extremely powerful and manipulative. They target Ron and Hermione because they are Harry's closest friends. By turning them against Harry, this antagonist hopes to isolate Harry and make him easier to defeat. The new antagonist could have some unique magical abilities that allow them to control the minds of others or create very convincing false scenarios.
Well, it could be that Lucius uses his powerful influence in the wizarding world. Maybe he intimidates Ron with threats related to his family's status or he uses some dark magic to create a distraction and whisk Hermione away.
Well, it could be that Snape has been secretly observing Ron's erratic behavior towards Hermione. When the situation gets out of hand, he intervenes. He might use his position as a teacher to discipline Ron and in the process, saves Hermione. Snape is a complex character with a lot of power and knowledge, so he could use various means like his occlumency skills to sense the danger Hermione is in and act accordingly.