He had his eyes on you ever since u started helping the new student earlier. During lunch break you're with the newbie again when suddenly Scara punched him. In the end everything resulted in a fight that didn't make sense to you.

"don't mess with her."

he seemed so indifferent and aggressive, but even without u having any reaction, he just left and later you discovered that the new student was harassing you behind your back taking photos of you. You hadn't realized that, but Scara did.