Enclosed crop before the beginning of December (8)
I believe the answer is:
cornered
'enclosed' is the definition.
(cornered can mean shut or enclosed in)
'crop before the beginning of december' is the wordplay.
'crop' becomes 'corn' (a farmer's crop of corn).
'before' becomes 'ere' (poetic term for 'before').
'the beginning of' says to take the initial letters.
The initial letter of 'december' is 'd'.
'corn'+'ere'+'d'='CORNERED'
(Other definitions for cornered that I've seen before include "went round the bend" , "Unable to escape" , "Monopolised the market" , "Put in a difficult position" , "Caught in position with no escape, like rat" .)