Bitterness constrains good cobblers (5)
I believe the answer is:
bilge
'bitterness constrains good cobblers' is the definition.
I can't judge whether this defines the answer.
'bitterness constrains good' is the wordplay.
'bitterness' becomes 'bile' (I've seen this in another clue).
'constrains' indicates putting letters inside.
'good' becomes 'g' (abbreviation).
'bile' going around 'g' is 'BILGE'.
Can you help me to learn more?
(Other definitions for bilge that I've seen before include "bull" , "Dirty water collecting on a vessel" , "Piffle - part of hull" , "Lower part of hull; nonsense" , "Nonsense (informal)" .)