Does try badly to ruin (7)
I believe the answer is:
destroy
'ruin' is the definition.
('destroy' can be a synonym of 'ruin')
'does try badly' is the wordplay.
'badly' is an anagram indicator.
'does'+'try'='doestry'
'doestry' anagrammed gives 'DESTROY'.
'to' acts as a link.
(Other definitions for destroy that I've seen before include "put to death" , "Annihilate" , "Get rid of" , "Flatten" , "Demolish; pull down" .)