"Linseed production", I put in, "is not my main occupation" (8)
I believe the answer is:
sideline
'not my main occupation' is the definition.
I can't tell whether this defines the answer.
'linseed production i put in' is the wordplay.
'production' indicates an anagram.
'put in' means one lot of letters goes inside another.
'linseed' anagrammed gives 'sidelne'.
'sidelne' enclosing 'i' is 'SIDELINE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for sideline that I've seen before include "second job" , "Spare-time activity" , "Take out of the picture" , "not my main interest" , "Secondary job" .)