Crumble gives autumn a role (4,5)
I believe the answer is:
fall apart
'crumble' is the definition.
(synonyms)
'autumn a role' is the wordplay.
'autumn' becomes 'fall' (synonyms).
'role' becomes 'part' (eg a part or role in a film).
'fall'+'a'+'part'='FALL APART'
'gives' is the link.
(Other definitions for fall apart that I've seen before include "Go to pieces" , "Come to pieces" , "Disintegrate" .)