Lacking cover, relative introduces a bizarre rule (2,7)
I believe the answer is:
au naturel
'lacking cover relative introduces a bizarre rule' is the definition.
I can't judge whether this defines the answer.
'relative introduces a bizarre rule' is the wordplay.
'relative' becomes 'aunt' (aunt is a kind of relative).
'introduces' indicates putting letters inside.
'bizarre' indicates an anagram.
'aunt' going around 'a' is 'aunat'.
'rule' anagrammed gives 'urel'.
'aunat'+'urel'='AU NATUREL'
Can you help me to learn more?
(Other definitions for au naturel that I've seen before include "may be exposed" , "Cooked plainly - naked" , "In the nude - in France" , "Naked in French, to aural tune" , "Nancy's naked" .)