Refuse to disallow capturing rook (4)
I believe the answer is:
bran
'refuse' is the definition.
(I've seen this before)
'disallow capturing rook' is the wordplay.
'disallow' becomes 'ban' (banning is a kind of disallowing).
'capturing' indicates putting letters inside.
'rook' becomes 'r' (abbreviation in chess).
'ban' placed around 'r' is 'BRAN'.
'to' is the link.
(Other definitions for bran that I've seen before include "Type of roughage" , "Refuse from grain" , "Fibre cereal" , "Husks of grain sifted from the flour" , "Horse-food in barn" .)