Crude comedy act's variable (7)
I believe the answer is:
sketchy
'crude' is the definition.
(thesaurus)
'comedy act's variable' is the wordplay.
'comedy act' becomes 'sketch' (a comedy sketch).
'variable' becomes 'y' (algebra).
'sketch'+'y'='SKETCHY'
(Other definitions for sketchy that I've seen before include "Imprecise" , "first draft" , "Superficial" , "Deep cave; evidence of road wear" , "Barely outlined" .)