Disastrous for soldier trapped in overturned vehicle (6)
I believe the answer is:
tragic
'disastrous' is the definition.
(thesaurus)
'soldier trapped in overturned vehicle' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue).
'trapped in' is an insertion indicator.
'overturned' shows that the letters should be reversed in order.
'vehicle' becomes 'cart' (cart is a kind of vehicle).
'cart' backwards is 'trac'.
'gi' going within 'trac' is 'TRAGIC'.
'for' is the link.
(Other definitions for tragic that I've seen before include "'Very, very sad (6)'" , "Deeply distressing" , "Involving grief of death or destruction" , "Shocking" , "Characterised by extreme distress or sorrow" .)