Let of speak of Eowyn, Niece of Theoden, Shield Maiden of Rohan, slayer of the Witch King of Angmar. The film version.
And how the shield she picks up is a prop much too thick and heavy for proper use.
Admittedly, you can see the classic round-shield grip on the back, but otherwise the thing looks like some primitive wheel. Some early-bronze-age solid wooden wheel with some kind of axle cap still attached.
Now where exactly would that have come from?
Well, the Orcs had brought a bunch of wheeled catapults. And normal catapults do not HAVE wheels because that's a terrible idea because you're supposed to set those things up in place, not set them up somewhere else and wheel them around like an idiot. The wheels are going to come off when it hits a bump. Or in the course of its normal operations. Those things have a strong kick.
So -- either the Orcs were a pack of morons and fired the catapults with the wheels still on, or they took the wheels off for battlefield operation.
And here comes Eowyn, sees that her dad's in bad trouble against the Witch King, doesn't have a shield, wait here's a wooden disc, must be a shield, grab.
That would explain why, in the movie, it's so thick and heavy and flies apart the instant it's hit. It was designed to withstand stress from one direction but not another. The Witch King's got a big ol' scary flail and a wheel can't handle that.
Which is why Eowyn's kind of flailing around, because she's using her training for shield tactics on something whose weight she didn't train for, so her own muscle memory is throwing her off-balance.
Plus, you know, she doesn't want to actually find out what happens if that horrifyingly large mass of iron actually hits her. Can't expect any valiant hero to be dumb enough to deal with that thing. But hey, that's why it looks like it does, right? A weapon to break morale more than anything. Doesn't even have to work very well as long as it makes the enemy run. The key word of "horrifyingly large" is "horrifying".
And it doesn't work very well on a physical basis, does it? It takes way too long to get the thing swinging into a proper back-the-fuck-off mode. And when it hits the dirt WHAM it keeps the Witch King busy long enough to give Eowyn a moment to recover.
The Witch King relied just a little too much on his usual terror tactics when he made that weapon. Also, you know, he didn't think any man could kill him.
(He really should have thought about how prophecies tend to be nitpicky with their wording.)
Hell, for all we know the flail is actually a cheap cast-iron prop, because the guy doesn't think anyone actually wants to try getting past it, because he doesn't think anyone is insane enough to actually get near him, because he doesn't think anyone would waste their time. Even if his weapon WAS made to withstand battle, the guy acts like anyone who relies on the fear of force: he has trouble dealing with someone that won't back down.
(Or two someones. Goddamn hobbits.)
If you look at the way he fights Eowyn, he's not being very efficient or clever. He tries to make his incredibly valuable mount do all the work, wastes it, tosses his flail around a lot instead of using it as a distraction from his sword, spins around like he's showboating and exposes his back to his opponent, finally gets in a lucky strike, grabs Eowyn by the throat and taunts her instead of just using the damn sword, never bothers to check his six o'clock, never even thinks of it, gets a knife in the knee from behind, kneels there in front of his opponent and doesn't keep fighting because he doesn't think he can die, gets stabbed right in the face. Way to go, buddy. Wonderful performance there.
Everything he does there looks like it's for intimidation. He has no idea how to actually fight. As soon as Eowyn hits the neck of the Fell Beast, he hesitates, because this twerp with the catapult wheel isn't running away like people are supposed to be running away from him. He's probably used to hitting running people from behind.
So he's like Shit shit shit what do I do, uh...the prop flail! That will work! That looks scary! Woosh! Woosh! Wham! Yeah! It worked! Alright now if I scare him away real good then he won't bother me anymore OW JEEZ WHAT WAS THAT. Dammit. Alright. I guess if I tell him he's wasting his time he'll move on wait it's a she. Dammit. Now was Glorfindel being general with his 'not by the hand of man shall he fall' bit or was he being specific OH GOD HE WAS BEING SPECIFIC.
The guy relied way too much on intimidation and that was his downfall. The very prophecy that he thought would protect him instead gave Eowyn the courage to overcome his terror.
And he shouldn't have been on the ground at all, because he's the commanding general of the entire host of Mordor. He has a job to do, and it really needs doing because his forces have lost the initiative by this point. He seriously needs to rally his troops, and he's wasting his time with his entire fight against Eowyn because Theoden is down and defeated; the only reason to even stay on the ground at that point is to make absolutely certain Theoden is dead -- otherwise the Witch King should be taking of his singular advantage over his enemy forces, which is his flying mount, which offers him a battlefield command position none of his enemies can reach. Unless it was very important to confirm the kill, the Witch King should have been moving on, or ideally never touching the earth at all.
Instead he wastes enough of his time to let Eowyn reach him, and then wastes more of his time deciding to actually fight her. He should have taken off the moment someone decided to challenge him.
And yet -- he couldn't do that, could he? Couldn't let anyone see the Witch King of Angmar run from some no-name soldier. He could run from Aragorn, from a Wizard, any sort of big foe is fair enough, but from some damn grunt? While everyone is watching? No way! That would have ruined his whole shtick forever. Ha ha, it's the Witch King, just wave a sword at him and he'll back off. This is a guy who relies on intimidation! Looking like a coward would ruin his primary battlefield weapon! No backing down from a challenge now.
Which is why he's doomed as soon as Dernhelm stands before him, because from that point forward the Witch King is bound to fight a battle he can't win.
He should never have let his Fell Beast touch the earth.