So after my disappointment over the 2nd Battle of Hoover Dam I started a new game (this time using Sawyers mod). After doing the usual things around Goodsprings, fighting the Powder Gangers, etc. I moseyed on down to Primm. This was my first encounter with the NCR (other than the dead guy you find in Devil's Gullet) and as I happily ran into the NCR camp outside the town they immediately opened fire on me and killed me. I was like WTF?! I reloaded and checked my stats, liked in Goodsprings, vilified by Powder Gang, but not even registered with the NCR yet, so I tried again, same result.

Why are they immediately hostile towards me when I've never met them before? I didn't have my weapons drawn and I wasn't wearing a faction uniform, so I can't figure out what's going on here.

Ringo is also in the NCR faction, Did you do anything to him? Only way i can see them attacking you that early is if you killed Ringo near them or if your wearing a NCRCF uniform.