Returning wanderer tackles source of evil spirit (6)
I believe the answer is:
daemon
'spirit' is the definition.
(I've seen this before)
'returning wanderer tackles source of evil' is the wordplay.
'returning' says the letters should be written in reverse.
'wanderer' becomes 'nomad' (nomad is a kind of wanderer).
'tackles' means one lot of letters goes inside another (tackle can mean to intercept or surround).
'source of' says to take the initial letters.
The initial letter of 'evil' is 'e'.
'nomad' enclosing 'e' is 'nomead'.
'nomead' backwards is 'DAEMON'.
(Other definitions for daemon that I've seen before include "Spirit in ancient Greek belief" , "guardian spirit" , "Evil spirit" .)