Yeah, I'm not sure what is surprising about that result. Kids like to play. Some times they get hurt doing so. Insofar as removing all rules I have some doubts, though it's more just what is left unsaid. Some rules are there to keep kids from abusing other kids (not that they don't still do that). Not enough detail is stated for me to assume anything though. Seems to me that kids started playing with what was around them (not surprising) and then ended up having fun (not surprising) but also made some mistakes (not surprising).
I had lots of injuries from play, but not at school. I do recall some one a little older than me telling a story about their elementary school (or some kind of thing camp maybe) where the kids were allowed to actually pry nails out of a tree stump with a hammer.
So many things here jump out at me. For one, learning how to actually do that is probably good for kids. At the same time my friend also said one kid just didn't get the idea and kept yanking only to finally jerk the nail out with so much force he ended up smacking another kid with the hammer (obviously a very different era). The general consensus was that the kid pulling on the nail was being obnoxious though rather than that some one should be sued.
My take was that something like that should probably be more supervised. Not all kids have innate mechanical skills or ability to anticipate things like that. But these days you couldn't even have something like that taught without drama. Seems like there has to be a balance between "who cares, let them do whatever" and "padded cell."
I was pretty scared of EVERYTHING as a kid, but I remember one of my favorite games (which was actually stupidly dangerous) was one we'd do when Girl Scouts got out (would have been on the church playground rather than at our school) as we waited for parents to get us. We'd get in an actual barrel one by one and take turns pushing each other down a slight hill in it. We actually had one of those safe padded playgrounds around. My childhood was full of those. But nothing soft and painted in primary colors could compare to the thrill of losing all sense of orientation and feeling the bizarre effects of physics. Not to mention the adrenaline rush, and the sense of pride one had upon emerging from the barrel alive... especially after that sick "OH GOD NO WHAT HAVE I DONE" moment when you first got in.
I know some one with kids now who was super upset because their child slipped on some ice in front of the school and fell down. No injuries. The kid was more embarrassed by the way their parent reacted than anything. I try to empathize since I don't have kids. I know it must be terrifying because there's always that tiny chance something really awful could happen. But your kid doesn't want to feel that afraid all of the time!