Accidentally Attacking "Good" Monsters

[Lanefan]

Outside of playing an evil campaign, I've never had a player attack a good NPC for good reasons. I've had a lot of jerk-holes attack good NPCs because "That's what my character would do!" but that's it.

That's not what the thread is asking though. Accidental attacks are what it's after, where the PCs never realize their target is a potential ally and-or just plain doesn't deserve to be attacked.

An example I DMed about 20-odd years ago: PC party is in the mountains and down some toughness so I decided to lob in an NPC Ranger for a while. Party had been travelling by night and sleeping by day, posting invisible sentries while at camp. So Ranger - a good upstanding sort - approaches and sees from a distance only three in-his-eyes-unguarded tents. Thinking this a bit suspicious he goes into stealth mode, and the party sentries completely fail to notice him as he sneaks up to a tent and looks inside.

In the tent is a sleeping PC, completely defenseless; so the Ranger gently wakes her up and asks a) if she's OK and b) why she is risking sleeping unguarded in such a dangerous area. The PC freaks out at a) the sight of a stranger in her tent and b) his inference that there's no guards outside. Two sentries (other PCs) hear the commotion and come racing in; the first tries to attack the Ranger and spectacularly fumbles, face-planting next to his feet. Before the Ranger can react beyond simply looking down the second PC-sentry puts a max-effect critical into his back, killing him instantly.

So yeah, it happens.

Lan-"to this day I remember the exact words I said next, through the palm covering my face: 'Nice going, guys - you just killed off your reinforcements.'"-efan