Railing if cooking bad at Rules (10)
I believe the answer is:
balustrade
'railing' is the definition.
(balustrade is a kind of railing)
'cooking bad at rules' is the wordplay.
'cooking' indicates an anagram (letters cooked up into a new form).
'bad'+'at'+'rules'='badatrules'
'badatrules' is an anagram of 'BALUSTRADE'.
'if' is the link.
(Other definitions for balustrade that I've seen before include "Row of pillars under rail" , "Railing at the side of a balcony" , "feature of terrace, perhaps" , "Stair rail and its supports" , "Railing on stairs or balcony" .)