Card acceptable in one half of Jersey (5)
I believe the answer is:
joker
'card' is the definition.
(joker is a type of playing card)
'acceptable in one half of jersey' is the wordplay.
'acceptable' becomes 'OK' (OK can mean acceptable or fine).
'in' is an insertion indicator.
'one half of' indicates taking half.
'jersey' halved is 'jer'.
'ok' going into 'jer' is 'JOKER'.
(Other definitions for joker that I've seen before include "Jester" , "Playing card" , "Comedian" , "may appear wild in play" , "Funny man in pack" .)