Revoking barrel regulation will bear fruit (6)
I believe the answer is:
walnut
'fruit' is the definition.
(walnut is a kind of fruit)
'revoking barrel regulation' is the wordplay.
'revoking' is a reversal indicator (to revoke is to reverse).
'barrel' becomes 'tun' (tun is a kind of barrel).
'regulation' becomes 'law' (I've seen this before).
'tun'+'law'='tunlaw'
'tunlaw' backwards is 'WALNUT'.
'will bear' acts as a link.
(Other definitions for walnut that I've seen before include "Decorative variety of wood" , "Tree, valuable ornamental wood" , "Wrinkled tree-fruit with a hard shell" , "Hard seed with furrowed shell" , "likely to get cracked at Christmas" .)