The forum rules can be found here:
https://forums.alliedmods.net/misc.php?do=showrules. They're shown during registration, and linked at the top and bottom of every page.
There have been some clarifications and minor additions over the years, but they're roughly the same as when this forum was founded 15 years ago. What's changed is we've got from always permanently banning, to temporary bans, and now to an automated system that informs you what rule was broken so you have a chance to correct your actions before being excluded from the forum.
There are "points" allocated to each rule so that everyone is treated equally, and the "infractions" expire (quite quickly) so that silly actions in the past don't affect you in the future.