In one of the Whiterun Companions quest to eliminate a Sabre Cat from Hod's House in Riverwood, you attack the cat and come outside after killing the beast. The town of Riverwood attacks you including the guards.


Now, if you do not attack the Sabre Cat and let the Whiterun guards and the NPC inside the house defeat the cat (you might have to run outside and let other guards kill it as well), you will still complete the quest, and be safe to head back out of Riverwood without anyone attacking you.

Just thought I would add the the long list of quest bugs.