The phrase I normally use is "Sword hung from his waste" or "sword at his waste" or the similar. They weren't really strapped, because you wanted a bit of movement since the drawing action isn't completely fluid with a strait sword.
I'm not saying they were hard to get out, it just wasn't a fluid motion like a katana, scimitar, sabre or other curved sword. Hence the scabbard had to move to let the sword out.
As for hangings, In theater I've used and drawn multiple types of swords from scabbards at the waste, from a sword belt I made my self. It was about an inch wide and loose. I hung it from about the stomach to the hip and could draw short, bastard and claymore sized swords.
It always surprised people that I could even get the last one out of there.