Todd Howard shares some details on Fallout 76's PvP https://www.pcgamer.com/fallout-76-pvp-guide/

"We want this element of danger, and it sounds weird to say, without griefing," Howard said.

Initially, damage scales down against another player who hasn't picked a fight with you. "When you shoot somebody you do a little bit of damage. You don't do full damage. It's like slapping somebody in a bar. You want to fight?"

"So you do little bits of damage. If you engage then you're doing full damage. And there's a cap reward based on the player's level. So if they player is really high level you're gonna get more caps than if they're low level. After one of them dies you can seek revenge which doubles the incentive."

"The player that kills somebody that didn't want to engage in [PvP] becomes a wanted murderer. They get no reward."

"So there is no reward, you get no caps, you get no XP, you get nothing for becoming a wanted murderer except for the kind of social incentives people have online to be assholes. We turn the assholes into interesting content. They appear on your map as a red star. Everybody sees them and they have a bounty on their head. And that bounty comes out of their own caps. And they can't see the other players on the map."

As a safeguard against accidentally starting a PvP situation with an inadvertent 'slap' to someone: there will be a "pacifist flag" players can activate so their bullets don't harm other players at all. Players who flag themselves as pacifists can still be killed, but you can ignore or block player after being killed by them once, so they can't see you on the map for the remainder of that session.