I wonder if there are cases on record of visitors to Ren Faires or Highland Games actually accidently cutting themselves, or someone else, with a knife or sword they brought or bought.
Like Jamie said, it's mostly just about insurance and liability. It's a sign of the times.

I disagree, though, that it's necessarily "common sense" for them to ban open blades. Back in the '70s, '80s, and '90s, I saw exposed blades all over the place at Ren faires. And it simply wasn't an issue. Either no one had common sense back then, or common sense today is different than it was then.

The only incident I ever saw was a guy who had his sword over his shoulder (balancing it with his hand in front) whirl around and almost hit a lady behind him. That could have been a nasty injury, as the blade likely would have slashed right across her mouth. Perhaps some of these incidents have actually led to injuries over the years, but if so, it's not been common enough that people know about it.

Aye, I think it has more to do with the organizers looking to cut down their insurance costs and make their lawyers happy. Which is sad.