Man taking traitor to be unpredictable (7)
I believe the answer is:
erratic
'unpredictable' is the definition.
(synonyms)
'man taking traitor' is the wordplay.
'man' becomes 'eric' (I've seen this before).
'taking' means one lot of letters goes inside another.
'traitor' becomes 'rat' (rat can mean a treacherous person).
'eric' placed around 'rat' is 'ERRATIC'.
'to be' acts as a link.
(Other definitions for erratic that I've seen before include "Hit-or-miss" , "Eccentric, aberrant" , "Random, unreliable" , "hit-and-miss" , "Unpredictable - car tire (anag)" .)