One was first to stand up in shop (4)
I believe the answer is:
deli
'in shop' is the definition.
(I've seen this before)
'one was first to stand up' is the wordplay.
'one' becomes 'i' (Roman numeral).
'was first' becomes 'led' (to lead is to go first).
'to stand up' shows that the letters should be reversed in order (in a down clue, the word stands upside down).
'i'+'led'='iled'
'iled' written backwards gives 'DELI'.
(Other definitions for deli that I've seen before include "Shop with unusual foods" , "Fine food shop" , "Fine-food store" , "place to buy food" , "food-store?" .)