Volunteer troops one commanded followed (6)
I believe the answer is:
tailed
'followed' is the definition.
(I've seen this before)
'volunteer troops one commanded' is the wordplay.
'volunteer troops' becomes 'TA' (Territorial Army).
'one' becomes 'I' (Roman numeral).
'commanded' becomes 'led' (I've seen this in another clue).
'ta'+'i'+'led'='TAILED'
(Other definitions for tailed that I've seen before include "Secretly followed" , "In slang, followed like private detective" , "Followed informally in detail" , "Followed, tracked" , "Dogged" .)