Ballbusting Camping

I've just arrived in a new camping,when some boys approach and ask me if i want to join a mixed wrestling tournament that is about to start in a tent. I try to refuse but they insist saying that they organize it every night and everyone enjoy a lot, so I end up accepting.

Once in the tent, a girl approaches me and asks me if I know the rules.
At my negative response she tells me: "There are no special rules, the purpose of fighting is to immobilize and to surrender the enemy. Only for the guys there is the special rule that if they are in distress but they are able to whistle, the antagonist must release them and resume the fighting.everything clear?".

I watch her, not understanding well the last rule, but at the end I accept.
After a few minutes i'm called in the middle of the tent for my fight.