There are two kids who do this at our playgroup. We avoid them as much as possible.
18mo or 2yo goes up to another one a similar age or a bit younger, and eye-gouges, grabs by the jaw or hair and pushes over, sinks teeth into arm so hard it draws blood, punches in the face so hard the other child falls off the chair, etc. It's unprovoked and the attacking kid doesn't seem upset, either before or after. It's also (in one case) almost always done when there's nobody else around.
18mo or just 2 is too young for this to be easily interpretable as the kid being a little thug who uses violence to get something. Also it's often done when the attacking child doesn't apparently want anything from the attacked child.
Anyone know how to interpret this usefully?