Here is a video from Sept 19. It shows how the Ukrainian troops have made decent gains, and divulges who their largest weapons supplier really is.
Their recent offensive in the eastern regions, demonstrates 21st century tactics, while the Russians seem to be stick somewhere in pre WW2, so far as their tactics are concerned.
The Russians expected the free Ukrainians to try to take the larger cities and towns in their counter attack.
The Ukraine didn't play that game. They seem to have bypassed and isolated the cities and strong points, creating a new version of siege warfare.
The key... Russia resupplies their trops almost entirely by rail. Their military truck fleet is relatively small.
If guerillas keep tearing up the rails, what can they do? They can't simply take a detour..as trucks would do..
So, Russian troops quartered in cities are likely short on supplies...and perhaps hungry.
Find out who is top arms supplier to the Ukraine (8+ min).
https://www.youtube.com/watch?v=W84tyE4l6JE