Strange case for experts (4)
I believe the answer is:
aces
'for experts' is the definition.
(ace is a kind of expert)
'strange case' is the wordplay.
'strange' is an anagram indicator.
'case' is an anagram of 'ACES'.
(Other definitions for aces that I've seen before include "Winning serves" , "Two will make deuce" , "Champions" , "holes in one" , "Unreturnable services" .)