Half the food in America produced by crafty types, the subject of conspiracy theorists! (4)
I believe the answer is:
ufos
'by crafty types the subject of conspiracy theorists' is the definition.
I can't judge whether this definition defines the answer.
'half the food in america' is the wordplay.
'half the' means to take half the letters.
'in' is an insertion indicator.
'america' becomes 'US' (United States).
'food' cut in half is 'fo'.
'fo' placed inside 'us' is 'UFOS'.
'produced' is the link.
Can you help me to learn more?
(Other definitions for ufos that I've seen before include "Mysterious objects in sky" , "Mysterious phenomena" , "Unauthorised traffic from outer space?" , "Initially, formal flying saucers" , "Potential alien craft" .)