Possible Clues:

• Foul callers, briefly
• Hall-of-famers Bill Klem and Nestor Chylak, e.g.
• Time callers
• Softball officials, briefly
• They know when you're out
• Boo targets, often
• Diamond quartet, briefly
• Experts on plays
• 'Steee-rike!' callers
• Calls balls and strikes