Is this kid mentally ill?

So I'm in 11th grade and have a classmate, who is so cruel that's I'm beginning to wonder if he's mentally healthy or not, here's some examples: yesterday at the PE he made some kids kneel and threw football ball at them several times with all his strength, and laughed when they were hurt, today he and his friend beat up my another classmate and video taped it, they think it's really entertaining and proudly uploaded it on facebook, commenting that they're gonna make another one, he also hits random kids in the stomach pretty often. I've seen a lot of bullies, but this case seems kinda different, why does he behave like that??