Unless a NATO member is attacked by Russia (such as Latvia or Estonia), these guys are just going to sit around and watch. Putin also knows it. He knows that the NATO can't do anything against him in Ukraine, other than supporting the corrupt oligarchs such as Tymoshenko and Akhmetov.
Well, NATO invaded Yugoslavia without Yugoslavia attacking or even threatening any NATO member first...
They could have successfully defended themselves, JNA (Yugoslav National Army) was almost intact after the NATO bombing finished, but their political leadership was corrupt and incapable. And that was the reason why NATO attacked Yugoslavia in the first place...