On your back is a less awkward way to carry an oversize sword, else you’d trip people with the sheath. Sometimes with really really really long swords, you can’t carry them at your waist at all - some are as long or longer than a man is tall, and would drag on the ground if you wore it at your waist. No, you’d normally want to carry it on your back, make your horse carry it, or carry it in a wagon.
Back in the day, you usually knew it when you were going into a big battle, so you could take the time to draw an enormous sword before the battle started. You’d have it in your hands as you went into battle, and you would actually use it more like a polearm than a sword.
A lot of video games and movies make it seem like you can draw a really long sword over your shoulder when it’s just not feasible. You would have to do it like Ned Stark does in the first episode. His sword Ice is quite oversized. There is zero way that Ned’s arm span would allow him to hold onto the sheath while drawing that sword all the way out, that’s why he has to have Theon hold the sheath while he draws it.
Jon Snow’s sword Longclaw is a bastard sword. It’s only a bit longer than a normal sword - he could draw it himself, but again, he’d have to take it off his back first. I looked around a bit for evidence.. in the last episode, he either has it already in his hand or he wears it at his waist, probably so he could draw it easily in case of Ygritte shenanigans.
I’d bet you a drink of the finest, finest booze that you’d never find an instance of Jon drawing that sword on-camera over his shoulder. Look at how long it is, it’s almost on the ground. I bet he’d have a hard time even drawing it from his waist.
I like how they had Sandor using the sword he wears at his waist during the riot - he had no time to take off his huge shoulder sword to undraw it, so he went for the quick draw. People did wear huge swords over their shoulder historically. My dismayed reaction in the other post was mostly bemusement / irritation that they made it seem like Sandor drew it over his shoulder when he went to fight Gregor, because the maneuver is impossible.
(Also, Sandor is never said in the books to have two swords, and it kind of bothers me. He resembles a sword rack a little bit. When would you ever need two swords? Either one or the other, Sandor. If he needed the enormous sword (for a big battle) he would know well in advance so he could go trade his normal sword for it. My question is, why does he wear it when he goes for the sword at his waist in an emergency anyway, and the dead weight sword on his back only hinders his movement? It doesn’t really make sense to me. I can only guess it’s just to look cool.
I wish he would trade his huge sword for a Clegane shield so it would resemble the book more and make more sense.)
Interesting wikipedia articles: Zweihänder - Two-handed sword - Nodachi