Soldiers need time picking up the scent (6)
I believe the answer is:
troops
'soldiers' is the definition.
(groups of soldiers)
'need time picking up the scent' is the wordplay.
'need time' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'picking up' shows that the letters should be reversed in order (in a down clue, letters go up).
'the scent' becomes 'spoor' (I've seen this before).
'spoor' back-to-front is 'roops'.
't'+'roops'='TROOPS'
Can you help me to learn more?
(Other definitions for troops that I've seen before include "men" , "Military divisions" , "Cavalry" , "Soldiers, armed forces" , "Bodies of soldiers" .)