Aunt Sally, say, is permissible target (4,4)
I believe the answer is:
fair game
'permissible target' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for fair game that I've seen before include "Aunt Sally, for instance" , "Legitimate target for attack or exploitation" , "Acceptable target?" , "permissible target" , "legitimate target for ridicule?" .)