I rode a Walker several years ago that we were looking after for a friend while he got his fences built. She was an unholy terror that would bite you if you turned to walk away, but she didn't buck. I'd offered to ride her to keep her in shape and I only ever made the mistake of riding her once. He'd been told she was green broke, which was fine. I've ridden several green broke horses over the years with few problems. But this girl, holy crap! Calling her green was the seller's nice way of saying she'd had some training under saddle and still didn't have the basics down. The first thing I do with a green horse is put them through the basics, but when I tried to get her to back she reared and tried to throw me off. I'll say this, I'm glad I saddled her myself or my butt would have been on the ground.
She wasn't the first the first Walker I'd ever ridden, but she was certainly the worst ride I've had. Aside from StarBuck bolting, but that was neither his fault nor mine.