I went to King’s Dominion recently and one of the rides (Dominator, I believe) this very nearly happened to the girl next to me, a friend of mine. It’s hard to say what would have happened - it may have been loosely secured - but they never checked the restraints (which they are supposed to do), and they never responded to us or noticed us as we were yelling for help. Going up the lift hill I managed to push down with enough force to lock it securely. It isn’t a sit-down coaster so that could have been problematic.
This is what happens when you employ and underpay generally indifferent teenagers to run your thrill rides, I’m afraid.
Had the employee told the woman she was too large to ride, Six Flgas would have been sued for discrimination... very large, Mexican woman.
Six Flags was screwed either way.