Comic hero is about ordinary one rowing (7)
I believe the answer is:
boatman
'one rowing' is the definition.
'comic hero is about ordinary' is the wordplay.
'comic hero' becomes 'batman'.
'is about' is an insertion indicator.
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'batman' going around 'o' is 'BOATMAN'.
(Other definitions for boatman that I've seen before include "Fellow with craft" , "One in charge of a small vessel" , "He may have a smack" , "Water transport provider" , "Rower - bargee" .)