Intervene to protect Charlie's treat (8)
I believe the answer is:
medicate
'treat' is the definition.
(I know that medicate is a more specific form of the action the treat)
'intervene to protect charlie's' is the wordplay.
'intervene' becomes 'mediate' (to mediate is to intervene between two parties).
'to protect' is an insertion indicator (inserted letters are held or protected).
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'mediate' placed around 'c' is 'MEDICATE'.
(Other definitions for medicate that I've seen before include "Supply drugs" , "Give a drug to" , "Treat with pills, drugs etc" , "Treat (one) with drugs" , "Administer a drug to" .)