Winners of a case, perhaps (4)
I believe the answer is:
aces
'winners' is the definition.
(I've seen this in another clue)
'case perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'case' is an anagram of 'ACES'.
'of a' is the link.
(Other definitions for aces that I've seen before include "wartime pilots?" , "Playing cards with single pips on their faces" , "Unreturnable services" , "never come back" , "Two will make deuce" .)