Sometimes enemy faction NPCs get stuck to the ground. They'll aggro, froth at the mouth, rage at you, but they can't move from their spawn spot.
Saw this on bleakers porch and a few other places (forget where specifically, but all were enemy NPCs on ground like bleakers porch).
Prior to noticing they were stuck, I had been using DK dark talons to root them, along with other magicka DK skills.
Not sure how to reproduce this, but I suspect the talons root isn't getting removed properly at times.
Angus of Noquar franchise.
And some others.