Starch thrown at a cop -- one's in for it! (7)
I believe the answer is:
tapioca
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'starch thrown at a cop one's in' is the wordplay.
'starch' becomes 'io' (I can't explain this - if you can you should believe this answer much more).
'thrown' indicates an anagram.
'a cop' becomes 'pc'.
'one' becomes 'a' (a thing is one thing).
'in' is an insertion indicator.
'at' with letters rearranged gives 'ta'.
'ta'+'pc'+'a'='tapca'
'io' inserted within 'tapca' is 'TAPIOCA'.
'for' is the link.
Can you help me to learn more?
(Other definitions for tapioca that I've seen before include "Sago pudding" , "Pudding maker" , "Cassava product used for puddings" , "Starchy dish" , "Pudding made from an extract of cassava" .)