Like the title says. If you're frustrated about the mobs not fighting back (you probably have a disease like believing in fair play, or maybe are also training armor skills like me), try this: cast an offensive spell at them, wait until you're attacked, then start attacking yourself. You'll be at a disadvantage in that you'll get hit once or twice without getting to retaliate, but so far it's been foolproof in getting mobs to attack me. Just to make sure, I tried attacking the creature in melee directly, without using magic first, would not get attacked even once.
By the by, it's unclear to me whether the creature needs to have hit you, or if a dodged attempt is good enough; I'm still getting hit every time, so I haven't been able to test it.
