Trainee soldier acted strangely (5)
I believe the answer is:
cadet
'trainee soldier' is the definition.
(I've seen this before)
'acted strangely' is the wordplay.
'strangely' indicates an anagram.
'acted' with letters rearranged gives 'CADET'.
(Other definitions for cadet that I've seen before include "Officer in training" , "who needs to be properly trained?" , "junior role" , "Younger son" , "Police or armed forces trainee" .)