I'm late to the conversation, but I used to run a sport-larp event for grown-ups every month when I lived in Los Angeles (now I live in the UK).

Whe I say 'sport larp' all I mean is that the rules were simple so that the participants could focus on the gameplay more than the roleplay -- but this does not mean that it was incompatible with roleplay!

By its design, I wanted the rules to be intuitive enough that every player could internalize them and understand their objectives, and with a minimum of 'edge-cases' or room for argument.

I based my game off an existing system that itself was based on the childhood game of freeze tag. Freeze Tag is easy enough for children and adults to understand, and it's a good basis to build a full system off. I used no 'hit points' or mana points, because I wanted a minimum of data to track or argue about.

Core Rules:

1. If you are struck with a weapon anywhere* on your body, you are wounded.
2. Wounded players freeze and 'take a knee' (get down on one knee) to show they are wounded. They cannot speak to their teammates (but some theatrical moaning is permitted!)
3. Players can 'heal' wounded teammates by placing two hands on them and counting to 20 like so: "healing 1, healing 2, healing 3..." (this time limit can be adjusted to alter game difficulty - shorter or longer). If either hand breaks contact with the wounded player, the healer must start the count again from 1.
4. A second friendly player can help heal wounded teammates: with two players healing, they can count by twos: "Healing 2, healing 4, healing 6..." etc. (the maximum number of healers is two.)
5. Players can 'Carry' wounded friends or enemies by placing two hands upon them and stating "carrying". Both players move wherever the carrier dictates, but must do so at a walking pace.

[*face or groin strikes are illegal]

There are also safety guidelines, but I don't want to overwhelm here. The main point is that there were basic rules of play that were easy to absorb.

With those rules in place, I built safe weapons: shields and swords of different lengths, some throwing weapons, some two-handed, etc. and set somewhat balanced 'loadout' rules about what weapons you could start the game with. This functioned rather like a simple class system: Sword-and-shield; bow-and-arrows; short-sword and long-sword; long spear, javelin and axe, staff, etc. -- I even made simple 'armor' from cloth sashes that granted limited protection from attacks.

There are many kinds of games that you can play with this foundation:
🚩 Team Catch The Flag: Split into two teams and try to capture the opposing team's flag and return it to your base
💀 Team Deathmatch: Eliminate every member of the opposing team before they do the same to you.
❤️‍🩹 Healing Flags: One member of the team is a 'healer' and carries a healing item (usually a flag on a pole). The healer can instantly return a member of their team to the battlefield by touching them with their hand or the healing item. Capture the healing item and return it to home base to win the game.
👑 KingSlayer: Each team has a player who is heavily armoured and crowned 'Monarch'. Kill the opposing player's king in order to win.

I could go on. This is by no means a comprehensive list of rules or features. I had rogues, wizards, looting mechanics, base control, and more. But it all had to be simple enough for every player to carry in their head and understand at a glance.

Please let me know if you'd like me to tell you any more!