Script not working? (ServerSided) ForceField Script Depending on team

You cannot access the LocalPlayer from the server, only on the client. Instead you would need to do something like this...

local Safe = game.Teams.Safe

game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:Connect(function(character)
        if player.Team == Safe then
            local forcefield = Instance.new("ForceField")
            forcefield.Name = "NewForceField"
            forcefield.Parent = character
        end
    end)
end

Alternatively this may not work due to the team being assigned when the character already exists, so you could also do something like this...

local Safe = game.Teams.Safe

game.Players.PlayerAdded:Connect(function(player)
    -- listen to when the player's team is changed
    player:GetPropertyChangedSignal("Team"):Connect(function()
        if player.Team == Safe then
            if player.Character then
                local forcefield = Instance.new("ForceField")
                forcefield.Name = "NewForceField"
                forcefield.Parent = player.Character
            end
        end
    end)
end