Adjudicator thwarted by a skilful better (10)
I believe the answer is:
preferable
'better' is the definition.
(thesaurus)
'adjudicator thwarted by a skilful' is the wordplay.
'adjudicator' becomes 'ref' (ref is a kind of adjudicator).
'thwarted by' is an insertion indicator (thwart could historically mean to pass across).
'a' becomes 'per'.
'skilful' becomes 'able' (I've seen this before).
'ref' inserted within 'per' is 'prefer'.
'prefer'+'able'='PREFERABLE'
(Other definitions for preferable that I've seen before include "more beneficial" , "Better" , "More desirable" .)