In retrospect mostly row about a row (3)
I believe the answer is:
oar
'row' is the definition.
(oar can mean to row with oars)
'in retrospect mostly row about a' is the wordplay.
'in retrospect' says the letters should be written backwards.
'mostly' means to remove the last letter.
'about' is an insertion indicator.
'row' with its last letter taken away is 'ro'.
'ro' placed around 'a' is 'rao'.
'rao' backwards is 'OAR'.
(Other definitions for oar that I've seen before include "Rower" , "Pusher" , "Rowing device" , "Scull" , "Crew member" .)