If a hostile NPC follows you over to their location they will attack them.
There are several pairs of Bruma Guards around town that are waiting to ambush a passing Dremora. If one approaches their location, one of them will pipe up.
- Bruma Guard: "One's coming. Wait until I give the signal."
When the Dremora gets close enough and passes them, the guard that spoke earlier yells.
- Bruma Guard: "Now!"