Left to occupy post, returning to Jersey (7)
I believe the answer is:
maillot
'jersey' is the definition.
(I've seen this before)
'left to occupy post returning to' is the wordplay.
'left' becomes 'l' (common abbreviation).
'to occupy' is an insertion indicator (I've seen this in other clues).
'post' becomes 'mail' (synonyms).
'returning' says the letters should be written backwards.
'to' written backwards gives 'ot'.
'l' inserted within 'mail' is 'maill'.
'maill'+'ot'='MAILLOT'
(Other definitions for maillot that I've seen before include "Swimsuit" , "Top" , "Jersey" , "Tights worn for ballet" .)