Cast is so grand for directors (4,5)
I believe the answer is:
road signs
'directors' is the definition.
(things which 'direct')
'cast is so grand' is the wordplay.
'cast' indicates anagramming the letters.
'is'+'so'+'grand'='issogrand'
'issogrand' anagrammed gives 'ROAD SIGNS'.
'for' is the link.
(Other definitions for road signs that I've seen before include "Indications for car driver to observe" , "pointers" .)