Small passion thats upsetting a worker (4,9)
I believe the answer is:
shop assistant
'a worker' is the definition.
(shop assistant is a kind of worker)
'small passion thats upsetting' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'upsetting' indicates an anagram.
'passion'+'thats'='passionthats'
'passionthats' with letters rearranged gives 'hopassistant'.
's'+'hopassistant'='SHOP-ASSISTANT'
(Other definitions for shop assistant that I've seen before include "who should be helping customers?" , "Worker in retail trade" , "one employed in store" , "Salesperson" , "Give grass to aid one" .)