Heartlessly ruined sketch (4)
I believe the answer is:
skit
'heartlessly ruined sketch' is the definition.
'skit' can be an answer for 'sketch' (thesaurus). I'm not sure about the 'heartlessly ruined' bit.
'heartlessly ruined sketch' is the wordplay.
'heartlessly' suggests removing the centre.
'ruined' becomes 'sunk' ('sunk' can be a synonym of 'ruined').
'sketch' becomes 'it' (I can't justify this - if you can you should believe this answer much more).
'sunk' with its middle removed is 'sk'.
'sk'+'it'='SKIT'
Can you help me to learn more?
(Other definitions for skit that I've seen before include "Turn" , "Opportunity to take off" , "Burlesque - parody" , "Hoax; satire" , "Brief satirical sketch" .)