If you render aid and something does go wrong then not only are you potentially opening the site up to a liability claim, you also open yourself to one. I know we don't live in quite the litigious society that exists in the US but it DOES happen.
Does it? I'd be genuinely fascinated to see UK case law on that. There may be some, I haven't checked for a while.
This is as good a time as any to remind airsoft
marshals that you are adopting a personal duty of care to the players, regardless of whether you know that, or even if you're being paid a penny. If you see something going badly wrong and don't act to stop it, you can personally be on the hook: see
Vowles vs Evans.
The main priority at a typical airsoft site will be to get a casualty out of the woods and to an area where they can receive better / professional aid.
There are three exceptions that spring to mind:
1. They're bleeding badly. But with geardos around, there's going something to hand that you can use to staunch it or form a tourniquet. Yes, there's the attendant risks of making it worse if you mess it up, which is why I agree that training trumps equipment.
2.
Charlie cops a saucepan in the throat. That means a set of airways in various sizes,
and someone who actually knows how to use them. I used to carry said set when I did group motorcycle ride-outs (where there's a fair chance of a passing medical professional stopping to assist), but it's such an edge case for airsoft that it doesn't seem worthwhile.
3. Cardiovascular, and specifically a myocardial infarction. The one thing I always carry for that, everywhere, is aspirin, and I'd advocate it for everyone. eBay "keyring pill holder" or similar, buy a bunch, pop a couple of aspirin in them and pass them out to friends and family, please.