One of the biggest concerns about Fallout 76 so far has been around how PvP will work, and if you can ignore it if you want to. Speaking at QuakeCon 2018, Bethesda Game Studios director Todd Howard broke down exactly how it would work.
Howard said Fallout 76 would be driven by both PvE and PvP, explaining that “we want this element of danger, and it sounds weird to say, without griefing.” How that works is that you have to actively respond to an attacking player in order to engage in PvP.
If you randomly start attacking another player you will do significantly less damage, which Howard described as “slapping someone in a bar” to challenge them to a fight. The damage only scales to normal levels if they then attack you back as a response. If not, you continue doing tiny damage.
Source: IGN.com Fallout 76 PvP Detailed, Aims for 'Danger Without Griefing'