Stick of rock? Not one Boatman supports (4)
I believe the answer is:
stab
'stick' is the definition.
(I've seen this in another clue)
'rock? not one boatman supports' is the wordplay.
'rock?' becomes 'sta' (I can't explain this - if you can you should give a lot more credence to this answer).
'not' is a deletion indicator.
'one' becomes 'a' (a thing is one thing).
'boatman' becomes 'ab' (abbreviation for able seaman).
'supports' says to put letters next to each other (bottom letters provide a support for the top ones).
'ab' with 'a' removed is 'b'.
'sta'+'b'='STAB'
'of' is the link.
(Other definitions for stab that I've seen before include "Sudden sharp feeling" , "Sudden sharp pain" , "shot in the dark?" , "Pierce with a knife" , "Inflict wound with knife" .)