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 an anagram.
'case' with letters rearranged gives 'ACES'.
'of a' acts as a 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" .)