A trainee soldier acted strangely (5)
I believe the answer is:
cadet
'a trainee soldier' is the definition.
(I've seen this before)
'acted strangely' is the wordplay.
'strangely' indicates an anagram.
'acted' is an anagram of 'CADET'.
(Other definitions for cadet that I've seen before include "One in training" , "Trainee -- acted (anag)" , "A trainee army officer" , "Military trainee officer" , "novice" .)