A hermit is one protected by both sides (5)
I believe the answer is:
loner
'a hermit' is the definition.
(I've seen this in other clues)
'one protected by both sides' is the wordplay.
'protected by' is an insertion indicator.
'both sides' becomes 'lr' (I've seen this in other clues).
'one' going inside 'lr' is 'LONER'.
'is' is the link.
(Other definitions for loner that I've seen before include "Solitary individual, prefers own company" , "He's not a joiner" , "Solitary person" , "Isolated individual" , "One shunning society" .)