I'm surprised US broadcaster limits alcohol (6)
I believe the answer is:
crumbs
'i'm surprised' is the definition.
(expression of surprise)
'us broadcaster limits alcohol' is the wordplay.
'us broadcaster' becomes 'cbs' (US TV network).
'limits' indicates putting letters inside (limit can mean to contain or block off).
'alcohol' becomes 'rum' (rum is a kind of alcohol).
'cbs' placed around 'rum' is 'CRUMBS'.
(Other definitions for crumbs that I've seen before include "Bits of bread - expression of dismay!" , "Crikey, cripes" , "Schoolboy expression (of comfort?)" , "Little things offering minimal comfort" , "Very little to eat -- goodness gracious me!" .)