“Pro-Ukrainian” fighters? lol. You mean a bunch of knowns butthurt over “fortress Bakhmut” who decided to terrorize grandmas and become a fertilizer?
What Bryansk doink?
How panik goink?
It’s an ancient tactic of warfare.
To raid the enemy where they are weak, in order to confuse, distract, and, if successful, cause a diversion of resources.
Both sides can do this at will, given that the tacitly undisputed front is so very long. Whether it will benefit both equally depends on other circumstances, such as the quality of intelligence available and the degree to which both have garrisoned their borders.
The Russians in this case seem to have left this border crossing, at least, poorly protected vs a company-batallion scale attack. And there doesn’t seem to have been a sufficient reaction force in range. The Ukrainians picked up on that, that’s the intelligence side of this.
The Russians could do the same, if they can figure out how to concentrate a raiding force without getting noticed, and to find a vulnerable crossing point.
Daily mail- Baghdad Bob.