Well, although most swordsmen would be unfamiliar with a boxing style, they would be plenty used to fighting other people with weapons, which are far more dangerous. They probably wouldn't be alive if they weren't quick enough to step away from an opening strike. Though ducking it may be a little unrealistic, as that's specifically a hand to hand skill.

What's great about your opponent dodging, and this is something most people overlook, is that it can be just as useful to force an opponent to dodge in the way you want then to hit them in the first place. I can think of a fair few fights where forcing a specific dodge from my opponent has earned me a better hit, or even the win.