Sailor supporting Judge in critical comment (3)
I believe the answer is:
jab
'critical comment' is the definition.
'sailor supporting judge' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'judge' becomes 'j'.
'ab' put after 'j' is 'JAB'.
'in' is the link.
(Other definitions for jab that I've seen before include "A short stiff punch" , "Short stiff blow or thrust" , "Inoculation" , "Short straight punch" , "Poke roughly or inject" .)