Raise petty objections when about six left (5)
I believe the answer is:
cavil
'raise petty objections' is the definition.
(I've seen this before)
'about six left' is the wordplay.
'about' becomes 'ca' (short for circa).
'six' becomes 'VI' (Roman numerals).
'left' becomes 'l' (common abbreviation).
'ca'+'vi'+'l'='CAVIL'
'when' acts as a link.
(Other definitions for cavil that I've seen before include "Complain" , "Find fault" , "Make trivial objection" , "Carp" , "Make petty objections" .)