Troops engaged in uphill jog suffering (7)
I believe the answer is:
torment
'suffering' is the definition.
(I know that torment is a type of suffering)
'troops engaged in uphill jog' is the wordplay.
'troops' becomes 'men' (men can mean soldiers).
'engaged in' is an insertion indicator.
'uphill' says the letters should be written in reverse (in a down clue, letters go up).
'jog' becomes 'trot' (synonyms).
'trot' in reverse letter order is 'tort'.
'men' going inside 'tort' is 'TORMENT'.
(Other definitions for torment that I've seen before include "Severe pain" , "Hound" , "Inflict pain on - pester" , "Severe physical or mental suffering" , "Torture" .)