Troop group not finishing course (7)
I believe the answer is:
regimen
'course' is the definition.
(prescribed course of treatment or diet)
'troop group not finishing' is the wordplay.
'troop group' becomes 'regiment' (I've seen this in another clue).
'not finishing' means to remove the last letter.
'regiment' with its final letter taken away is 'REGIMEN'.
(Other definitions for regimen that I've seen before include "Prescribed way of life like diet" , "Disciplined system" , "Prescribed course of diet, exercise, etc" , "discipline" , "Systematic course of treatment, diet, etc" .)