Pitiable soldier in cart upset (6)
I believe the answer is:
tragic
'pitiable' is the definition.
(I've seen this before)
'soldier in cart upset' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'in' means one lot of letters goes inside another.
'upset' shows that the letters should be reversed in order.
'cart' written backwards gives 'trac'.
'gi' going inside 'trac' is 'TRAGIC'.
(Other definitions for tragic that I've seen before include "Shocking" , "Resulting in great loss" , "Grievous" , "Extremely sad and distressing" , "Very sad; Schubert's 4th symphony nickname" .)