Percy said something very impolite that he would in other circumstances have reprimanded any of his siblings for saying within earshot of a first-year. Then, he did something which was impossibly brave and which he would later decide had been impossibly stupid: he ran into the room and placed himself squarely between the troll and the girl. She was crying and bleeding and definitely had some broken bones and clearly would not survive a second hit from that club, and even later when he thought about it, he didn't think he could possibly have done anything else, stupid as it had been. You don't abandon frightened eleven-year-old girls to trolls, you just - you just don't.