Related Clues:

• Ref's cohort
• Call, as a game
• Ump's colleague
• Sports 'zebra'
• Fight figure
• Round figure?
• Call the shots?
• Paid whistle blower
• Whistle-blower?
• Short mediator
• Diamond expert
• Arbitrator
• Mat slapper
• Field worker
• One who may O.K. a KO