Umpire from America left in denial (7)
I believe the answer is:
refusal
'denial' is the definition.
(refusal is a kind of denial)
'umpire from america left' is the wordplay.
'umpire' becomes 'ref' (short for referee).
'from america' becomes 'US' (United States).
'left' becomes 'al' (I've seen this in other clues).
'ref'+'us'+'al'='REFUSAL'
'in' acts as a link.
(Other definitions for refusal that I've seen before include "Act of a horse stopping short at a jump" , "The turning down of a request" , "Chance to decline" , "The act of saying no" , "Act of declining to take or accept something" .)