The way she lifted the knight.. made me wonder if knights in our past could do judo-like moves on armordressed enemies?
plus
the heaviest armor could be around 40 Kilogram or more so it is alot of weigh that can pin them down if they fall to the ground.
so no wonder about that they got surprised she could lift that guy.
To add some detail to what everyone else has said, yes. That's exactly how you're
supposed to take down a fully armored knight. Outside of things like heavy axes, war picks, and so on, which are what you want to use if you need to open a man like a can of tuna, you get three or four buddies, and you tackle that big ol' bastard to the ground, and just hold him there while a friend sticks a dagger between plates until the knight stops moving.
The '40kg armor' is actually some of the heaviest armor you'd ever see, the kind of thing most knights would only wear at tournaments fighting other knights. The average field harness(which is what we call 'full plate mail', with 'mail' actually referring specifically to 'chain mail') is much lighter, around 15~25kg, and hardly any less protective. The extra plates and metal on the heavier sets is mostly there to keep that lance from absolutely annihilating your shoulder during a joust, but the extra mobility from the lighter sets more than makes up for the somewhat lower protectiveness of the thinner plates while on the field.
You'd think you'd want as much protection as possible, but that's only true up to a certain point. Early fire arms and full plate harnesses were contemporary, and plate armor
did protect against them fairly well. The problem comes a little later when you've got far more, and more powerful, firearms on the field and it becomes substantially less worth it to be slowed, however marginally, by the armor. That's why later soldiers, even the elite ones like knights, start dropping most parts of the plate armor and eventually end up only with a breastplate and helmet.
But for knights on the field? Grappling is the way to go. Grab their arms and put them into arm locks so you can stick a knife through their arm pits, trip them and sit on their chests and stick knives through visors and between the helmet and gorget(neck protection), put spears through the backs of their knees, etc.
Defeating plate armor without weapons specifically designed for it is all about attacking the joints, and that's way easier when you got a bunch of other guys holding him down, or you twist his joints so he can't throw you off.
This is why you keep hearing about footwork in martial arts stories, though. Keeping your footing is functionally keeping your life. You get tripped, you get thrown off balance, whatever, you're dead. It applies whether you're in armor or not. You do not want to be on your ass when a dude is trying to stick something sharp and pointy somewhere soft and squishy.
Funnily enough, this is also exactly where women excel in hand to hand combat. The lower center of gravity that comes from wider hips gives women a great base to work from for throwing people to the ground and keeping their own balance. I think the manga actually talked about that a little in one of the earlier chapters?
