It’s sad when a soldier’s in the cart, perhaps (6)
I believe the answer is:
tragic
'it's sad' is the definition.
(I've seen this before)
'a soldier's in the cart perhaps' is the wordplay.
'a soldier' becomes 'gi' (government issue or general issue).
'in the' means one lot of letters goes inside another.
'perhaps' indicates anagramming the letters.
'cart' is an anagram of 'trac'.
'gi' put within 'trac' is 'TRAGIC'.
'when' acts as a link.
(Other definitions for tragic that I've seen before include "Terribly sad and distressing" , "Heart-rending" , "Grievous" , "like King Lear" , "Ill-fated" .)