"Nobody Knows Why A Random NPC In Red Dead Redemption II Suddenly Became A Murderer"

Kotaku:

The clip was posted by Reddit user DMarlow310 and within a few hours was one of the most upvoted posts on the Red Dead subreddit that day. The title of the post intrigued me. Someone claiming to see something totally new in Red Dead Redemption II is usually followed by a photo or clip of something I’ve seen before or can easily explain. Not this time.

...

If you watch closely, you can see the murderer run towards the fight before he stops and slows down, creeping behind the angry NPC.

But more interestingly, if you watch towards the back of the area, you can see the moment the murderer decides to intervene. It happens right before the first punch. He whips around and begins running towards the fight.