I rouse fools with cunning, no joking (9)
I believe the answer is:
seriously
'no joking' is the definition.
(without joking or silliness)
'i rouse fools with cunning' is the wordplay.
'fools' indicates an anagram (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'cunning' becomes 'sly' (synonyms).
'i'+'rouse'='irouse'
'irouse' with letters rearranged gives 'seriou'.
'seriou'+'sly'='SERIOUSLY'
(Other definitions for seriously that I've seen before include "In a solemn and thoughtful manner" , "Gravely" .)