Stun

The stun skill is a rogue skill that involves a sneaky rogue, a heavy blunt
object (i.e. a rock or something) and the back of someone's head. Once the
victim awakes again, they often find their personal belongings missing. That
is, if they ever wake again at all.

The classes that get the skill stun are:

assassin   : Level  24 (excellent)
rogue      : Level  21 (excellent)