Possible Clues:

• Person revealing improper activities
• Grass — you'll see a referee here
• Referee with his belt turning to cow?
• Person with inside information making public some illicit activity
• One who informs a referee?
• Informer, one stopping game?
• One peeping at something secret?
• Referee observing grass
• Exposer of bad things -- one telling us the game's over?
• Tell-tale phone call coming earlier