Referee (one hoping to ensure the game is up?) (7-6)
I believe the answer is:
whistle-blower
(Other definitions for whistle-blower that I've seen before include "Person with inside information making public some illicit activity" , "Informant on malpractice" , "One who exposes wrongdoing" , "One who informs on malpractice" , "Teller of tales to the authorities - referee?" .)