Deny an umpire employment (6)
I believe the answer is:
refuse
'deny' is the definition.
(deny can mean to refuse or reject)
'an umpire employment' is the wordplay.
'an umpire' becomes 'ref' (short for referee).
'employment' becomes 'use' (how something is used).
'ref'+'use'='REFUSE'
(Other definitions for refuse that I've seen before include "Say no to - rubbish" , "Junk" , "Reject the waste material" , "Don't take the rubbish" , "Say no to garbage" .)