[Pon]

Ok, on the offchance that this might help someone else finish it off, here's what i was trying to do:

local c = Collection()

nonades = trigger_ff_script:new({})

function nonades:ontouch( touch_entity )
	if IsPlayer( touch_entity ) then
		local player = CastToPlayer( touch_entity )
		-- Add this player to the collection
		c:AddItem( player )
	end
end


function nonades:onendtouch( touch_entity )
	if IsPlayer( touch_entity ) then
		local player = CastToPlayer( touch_entity )
		-- Remove player from collection
		c:RemoveItem( player )
	end	
end


-- This is fired when everyone has stopped touching "nonades"
-- and it goes to its inactive state
function nonades:oninactive()
	-- Clear out the items in the collection
	c:RemoveAllItems()
end



function player_onthrowgren2(player, prime)

	if c:Count() == 0 then
		return EVENT_ALLOWED
	end

	for temp in c.items do
		local c_player = CastToPlayer( temp )
		
		if c_player == player then
			return EVENT_DISALLOWED
		end
	end

	return EVENT_ALLOWED
end

Didn't work, however using a gren inside the nonades area did produce an error, whereas using it outside of it did not... so it must be on the right track, I think.