Gabbi, who had been walking slightly in front of them, must have heard, because in one swift movement she had dropped all her books, swung around, grabbed Malfoy by the neck and slammed him into the stone corridor wall.

"NEVER... EVER... INSULT... MY... SISTER!!!!" She spat the words out, one at a time, as if they tasted bad on her lips.
A trickle of blood was running down the wall behind Malfoy. He had been knocked out. Gabbi didn't seem to have noticed this, as she slammed him again and again into the wall. A crowd had gathered around the pair of them by this time, although the people in the front were at least 20 feet away. No one seemed to want to go near the seemingly mad girl, as she slugged Malfoy in the shoulder once, twice, three times.
Professor Sinistra was the first teacher to reach Gabbi. She cut through the crowd, all the while yelling at Gabbi to let go of Malfoy, who now also sustained a broken collar bone. Gabbi heard the yells, and swung her head around to look at the Professor, who had broken through the crowd at last. Gabbi's blue eyes were shooting death looks at anyone who made eye contact.
With a wave of her hand, Gabbi sent Professor Sinistra flying down the corridor 50 feet, landing tangled in a suit of armor.