It’s not just being trained to fight, it’s the experience of fighting. SCA gets you used to getting hit with a heavy rattan stick disguised as a sword-like object, with safety rules and armor. Most martial arts classes get you used to “fighting” with both explicit and implicit rules and safety measures so you don’t break your partners. Even MMA has extensive safety regulations. Experience counts for a lot. Experience with killing and maiming people is something that, unless you’re in the military or a criminal, none of us has.
Any knight has been through battles. Lots of ‘em. As a squire, he would have both observed combat and may have been involved in the battles in some way himself. Play for this class was barely distinguishable from battle. Hunting, tourneys, games of skill and strength were routine pursuits. They were also effectively the police and national guard. If there was a bar fight, for example, it was pretty much their job to stop it.
Now on one side, there’s your average cubicle dweller, whose idea of “exercise” is to jog a couple of miles and maybe lift some moderately heavy weights. On the other side, there’s a guy who probably was in more fights by the age of 15 than any of us ever has in his entire life, and who has killed dozens, if not hundreds, in physical combat. Not all of his fights were in armor and with weapons. It is highly likely that he had been in life and death fights without being armed, and like I said earlier, recreation for these guys was basically brawling.
I have no reason to believe that they did training much different hundreds of years ago than the traditions that have been handed down from that time. Even in the dedicated sword schools, there are unarmed techniques, and in many of them, you learn the unarmed stuff first, before you even get to hold a sword or sword-like object; one of the overlaps between Western and Eastern martial arts is sparring with wooden swords. Grappling and even striking was integrated into the combat training, as shown by extant training manuals. Going from what I know about similar manuals in Eastern martial arts, a lot of the details of what was known didn’t make it into writing. The comments and drawings are more of a broad-strokes guideline to support memory.
So, he’s got experience, he does have training, and if he’s a knight, he has survived literally years of people trying to kill him — and years of his peers trying to get him killed doing dangerous shit like going boar hunting with a spear. The most inept out of shape knight in Europe would easily be more than a match for more than 90% of the populace now. People with training and physical ability might, just might survive. Everyone else is a corpse waiting to happen.