Being sorry, destroy force (5)
I believe the answer is:
ruing
'being sorry' is the definition.
(to rue is to regret or feel sorrow)
'destroy force' is the wordplay.
'destroy' becomes 'ruin' (synonyms).
'force' becomes 'G' (short for gravity).
'ruin'+'g'='RUING'
(Other definitions for ruing that I've seen before include "feeling remorse" , "Having second thoughts" , "Feeling bad" , "full of remorse?" , "Feeling sorry for" .)