Writer might cry out, audibly on reaching headland (9)
I believe the answer is:
ballpoint
'writer' is the definition.
(writing implement)
'cry out audibly on reaching headland' is the wordplay.
'cry out' becomes 'bawl'.
'audibly' shows a homophone (sound like).
'on reaching headland' becomes 'point' (I am not sure about this - if you are sure you should believe this answer much more).
'bawl' sounds like 'ball'.
'ball'+'point'='BALLPOINT'
'might' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ballpoint that I've seen before include "Writer" , "Type of pen" , "Biro" .)