Do you see Hungary, Slovakia, or Turkey fighting Russia? And I can continue with other examples. NATO can't shoot a bullet if there's a single country against. I can't see even the US entering the fight, Trump is a coward grifter that hits only weak opponents.
Why not NATO against CSTO? Do you know that Russia has its own NATO equivalent?
Right now Russia is armed by North Korea (soldiers included), Iran (weaponry and components) and China (components, machine tools, etc).
About a week ago, Russia threatened Austria with an invasion and Austria isn't in NATO.
See, it gets pretty awkward when you think about it. There will be no NATO Vs Russia.