Act to cover renegade (8)
I believe the answer is:
turncoat
'renegade' is the definition.
(synonyms)
'act to cover' is the wordplay.
'act' becomes 'turn' (a routine or performance).
'to cover' becomes 'coat' (coating is a kind of covering).
'turn'+'coat'='TURNCOAT'
(Other definitions for turncoat that I've seen before include "Rat" , "Deserter to opposition" , "'Renegade, traitor (8)'" , "treacherous as one?" , "Judas" .)