Criticism at change of course (6)
I believe the answer is:
attack
'criticism' is the definition.
(attack is a kind of criticism)
'at change of course' is the wordplay.
'change of course' becomes 'tack' (tack is a kind of change of course).
'at'+'tack'='ATTACK'
(Other definitions for attack that I've seen before include "Show aggression" , "Set upon" , "Brownish pigment" , "Offensive move" , "Raid" .)