You're also probably discounting what peasant style manual labor (and hobbies, which include beating the shit out of each other with fists, clubs, etc) does for your combat ability. Hand and wrist strength is a huge deal in pre-firearms days, and peasants were at least 3-4 standard deviations stronger in these ways than average people now (really: that much -I've fooled around with building hand strength and it's bonkers how strong people can get in this domain). People basically exerted their strength through simple hafted tools all day; makes them good at exerting their strength through simple hafted tools all day. Regarding group tactics; peasants had lots of games which could have helped them with this. For example, Hurling[0], and I'm sure there was lots of stuff like Calcio Storico[1].
The real advantage the knights had (beyond equipment, like horses and the morale of feeling superior to the peasant) was probably nutrition. They spent most of their downtime hunting, feasting and eating meat, and between wearing heavy armor and their strength oriented workouts, the knights were probably pretty jacked. 50 or 100lbs of muscle and fat and 6-8" of height helps a lot. I don't have references in front of me for this, but David Willoughby talks about some of this in his book, and I'm sure you can see it in skeletons of Nobles versus peasants (aka Nobles will have larger skeletons with 'deformities' at the muscle attachment points).
That would be the Melee [1]:
"Tournaments often contained a mêlée consisting of knights fighting one another on foot or mounted, either divided into two sides or fighting as a free-for-all. "
[1] https://en.wikipedia.org/wiki/Tournament_(medieval)#Melee
To sell you on it a bit: if you've lifted for ~10 years you've probably hit your biological peak on the big exercises, and you've gone into some kind of maintenance mode, or are concentrating more on strength endurance, or rotating through peak efforts on different kinds of strength, or working around inevitable injuries or whatever. Either way, a man gets bored, and a large part of the appeal of strength training is the feeling of making progress. Various forms of hand strength; there's basically infinite potential there. Leonardo used to bend horseshoes, and it's a seemingly impossible feat I think most men are capable of with some training. It's also something available to old people who might not be able or willing to pull 5 wheels on the deadlift any more. You can, of course, injure your hands or forearms, but your chances of being crippled by it are fairly low. The other thing about it; you can train a fair amount (unlike big lifts) without blowing out your cortisol, but you get that intense triumphant grrrrrrr ogre nerve energy from doing it that you do after a max effort lift. Also it looks cool and chicks and small children dig it when you do seemingly impossible feats.
Anyway, peasants who hoed their crops and lifted bricks all day were fucking STRONG in the hands. Probably stronger than most nobles in that regard.
[0] https://www.gripboard.com/index.php?/forum/7-workout-reports...
So without legs? Just pure hands?
This story is attributed to Jean de Maingre.
I guess they did train that movement specifically (in armor etc.), because it's not something you could just randomly do on a whim even if you are very strong. Definitely not something you would WANT to do on a whim if you can fall down to your death and also have to be in good enough shape after to fight (which makes this particularly crazy).
Damn, considering that they were also trained grapplers, those must have been one hell of sparring partners.
I can’t imagine how 10+ years of training could not give a knight an infinite advantage even if we equalize the combatants in terms of equipment.
Also knights were training to fight since they were children, so in our hypothetical bar fight the pro-fighter’s skills would be along the lines of those of Floyd Mayweather (who started training when he was 9). Surely the knight may be less gifted, but that matter should really concern other knights and not peasants :)
49 vs 9000 scenario described in the post seems grotesque but I think, limiting the number of slain civilians by knights’ stamina and assuming that any resistance is negligible is more than reasonable.