March in poor formation behind junction (5)
I believe the answer is:
troop
'march' is the definition.
(I know that troop is a more specific form of the action march)
'poor formation behind junction' is the wordplay.
'formation' indicates anagramming the letters.
'behind' is a charade indicator (letters next to each other).
'junction' becomes 't'.
'poor' anagrammed gives 'roop'.
'roop' after 't' is 'TROOP'.
'in' acts as a link.
(Other definitions for troop that I've seen before include "A company, unit" , "Parade" , "Band of people" , "Flock, crowd" , "Group of, eg, monkeys" .)