Cold-hearted umpire's decision, with lousy sides eliminated (7)
I believe the answer is:
callous
'cold-hearted' is the definition.
(thesaurus)
'umpire's decision with lousy sides eliminated' is the wordplay.
I cannot quite see how this works, but
'decision' could be 'call' (call is a kind of decision) and 'call' is found within the answer.
The remaining letters 'ous' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for callous that I've seen before include "Hard-hearted" , "Not feeling" , "Hard and unfeeling" , "Emotionally hardened" , "Cruel or unsympathetic" .)