When rules are mandatory, what's "open" about it?
Discussion
You can exit, opt out.
Sports federations figured this out long ago. Nobody wants to watch a sport if competitors can break the rules at will. If competitors don’t like the rules, they can set up their own league, own rule. If the premise is “no rules”, that’s perfectly fine, too.
Also, nation states figured this out long ago as well, That’s why they have border controls and legal tender. It’s the opposite of “open”. And, in this case, you can always still exit (if the state doesn’t have exit controls).