Okay, I've had two random encounters at the same time, at the same spot before, but this one was... simply WTF.
I don't know exactly what happened, but when I left Markarth for Dead Crone Rock, seven or eight red dots suddenly appeared on my compass. I immediately became alarmed, and approached with caution. When I saw what was going on, I had serious trouble believing my eyes: I spotted Vilkas and Ria fighting a bunch of Forsworn
and what looked like bandits. It was fourteen against two...needless to say, I jumped right in.
Pictured below is the outcome. I counted 8 Forsworn, 6 Orc Hunters (not bandits, after all) and the Sabre Cat.
It's as if three events had occurred all at once, since the Forsworn vs. Orc Hunters usually involves three or four of each.