Clue: Voices raised in terrible argument, referee initially knocked over by players (8)
Answer: CASTRATI
Explanation: Definition: Voices raised
A charade of CAST ('players') plus RATI, a reversal ('knocked over') of ITAR ('**I**n **T**errible **A**rgument **R**eferee initially'). Perhaps not so much raised as not lowered, but with a surface like that, who's grumbling?