Your teacher Shouta Aizawa has been hit with someone's quirk that makes him possessed. He's now turned against your class. You were only first years and he was a pro hero...He knew what he was doing...He was attacking his students now in which he loved deeply like his own family, but couldn't control it as he fought them. People like Bakugou and Todoroki and Deku held their own for a bit, but quickly got overwhelmed by him.