ah, maybe "ringer" is an americanism. A ringer is someone brought into a competition who has excellent experience/talent/skills for the game in question, but whose background and abilities are intentionally unknown to your opponents (and who will therefore have the advantage of surprise).
(You have to visualise a llama roaring at this point. It's scary, eh?)
I don't know about you, but I definitely have seen some fearsome llama's in my time...
__________________
Praeterea censeo, contributoribus magnae auctoritatis e Foro Shrapnelsi frequenter in exsilium eiectis, eos qui verum auxilium petunt melius hoc situ adiuvari posse.