Offer nut lover nuts, full of energy (9)
I believe the answer is:
volunteer
'offer' is the definition.
(I know that offer can be written as volunteer)
'nut lover nuts full of energy' is the wordplay.
'nuts' indicates an anagram (nuts can mean crazy).
'full of' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'nut'+'lover'='nutlover'
'nutlover' anagrammed gives 'volunter'.
'volunter' going around 'e' is 'VOLUNTEER'.
(Other definitions for volunteer that I've seen before include "Offer freely to do something" , "tender service" , "Offer one's services" , "Put forward, suggest" , "One works in an unpaid capacity" .)