MotionBlur: The right way.

if (CLIENT) then
    local ply = LocalPlayer()
    local health
    local AdditiveAlpha = 0.1
    local DrawAlpha = 0.79
    local FrameUpdateDelay = 0.05
    hook.Add("RenderScreenspaceEffects", "Realism_Blur", function()
        health = ply:Health()
        if health < 30 then
            DrawMotionBlur( AdditiveAlpha, DrawAlpha, FrameUpdateDelay )
        end
    end)
end