Tore up bank contract (6)
I believe the answer is:
narrow
'contract' is the definition.
(I know that contract can be written as narrow)
'tore up bank' is the wordplay.
'tore' becomes 'ran' (I've seen this before).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'bank' becomes 'row' (a bank is a row of things).
'ran' written backwards gives 'nar'.
'nar'+'row'='NARROW'
(Other definitions for narrow that I've seen before include "Lacking tolerance" , "Closely confining" , "Strait, not broad" , "Constricted in width" , "Restrict" .)