If you've ever watched an Olympic fencing bout, you have some idea of how wicked-fast the action is. I had the privilege of taking a couple of years of fencing in college under Dr. Francis Zold [1], captain of the 1948 Hungarian Olympic team, and, over thirty years later, and even against people who'd actually picked up and trained with a foil, epee, or saber, he was ridonculously quick and competent.
These people are fighting with saber, which is unique in fencing weapons in allowing a point with either the tip or the edge of the blade, anywhere from the waist up.
It does not go well for the amateurs, even under the maxim of "the world's best swordsman doesn't fear the second-best swordsman, but the worst."
[1] http://museumofamericanfencing.com/wp/zold-dr-francis/
Ayup.
One of the guys I do rapier fencing with was a national top-5 sabre fencer in his younger days. Twitchy twitchy fast reflexes.
What's always interesting to me is seeing what happens when we put one of our swords in the hands of a capable modern fencer to watch them adapt to the new weapon and rules.
My roommate and I took fencing together in college. I stopped after a semester. He's still doing and teaching it–but SCA-style. I would not want to come close to him with a blade.