So what's the dirtiest but technically still legal tactic you've witnessed? A long time ago playing recreational capture the flag, one of the dudes (small old man over 60) on the other team sauntered down the middle of the field towards the player out area. Which was behind where our flag was. No one batted an eyelid at him because we assumed he was out, but as soon as he was in our flag area the flag, he turned and advanced back to his own base shooting out our entire team from the back. Well, we should have known better because his marker wasn't in the air, but no-one I guess wanted to shoot an old man needlessly 'just to make sure.'