It's not just that latency causes the guy on the end to be nearer to you than he actually appears (like I've read up about in the past), but more importantly that latency causes your character's position information to be updated at a much slower rate on their screen than yours.
Let x represent the foe, let o represent you on your screen and let q represent your character's lagging model on their screen. Underscores are just for distancing of the respective symbols.
I noticed this while trying out my halberd in the kiln since I wasn't used to the hit timings on the thing (new weapon lol).
There was this Russian guy who was constantly running for my back while I backpedalled, and he would always get the lagstab by suddenly breaking off from me and circling an invisible target several steps to my front where I'd been a number of seconds ago- and then he'd land the OHKO backstab (zoomed in lol). For a long time now I'd wondered why people said that backpedaling worked at preventing lagstabbers, and why it never seemed to work for me against lock bs fishers (backpedaling gets me lagstabbed without fail; instead I get rid of lagstabbers by counter-bsing or hitting behind me when I predict a lstab attempt). I finally got around to thinking about it yesterday when I met this guy.
Basically, when you're backpedaling you move at an extremely slow velocity as compared to your opponent while he's running for your back. At some point the connection will be slow to update your character information, causing you to freeze in place or move more slowly than actual (a.k.a lag spike)- giving him the opportunity to easily circle the image of your character on his screen with his momentum advantage to nab the lagstab.
So how do you get rid of this, if you want to backpedal? You watch for when they appear to break lock and follow an invisible image of you then you hit them. Backpedaling, on its own, is useless as a safeguard. You have to combine it with other things like counter-bsing and null damage bs for it to work.
Of course, this takes a lot of precise timing, aiming and watching for their exact movements as they are also lagging on your screen. I've noticed that sometimes they are a spear's length away when they land the lagstab in this way and sometimes they are a falchion's distance away.
Thoughts? Comments? Improvements? Am I dreadfully wrong? Anything I've missed out?