After small operation, sit for painter and counter (6)
I believe the answer is:
oppose
'counter' is the definition.
(I've seen this before)
'after small operation sit' is the wordplay.
'after' means one lot of letters go next to another.
'small operation' becomes 'op' ('small' suggests a short form).
'sit' becomes 'pose' (synonyms).
'op' next to 'pose' is 'OPPOSE'.
'for painter and' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for oppose that I've seen before include "match" , "Bar" , "Compete with" , "Obstruct, resist" , "Take stand against, resist" .)