Boasts, sent off to lookout post (5-4)
I believe the answer is:
crows-nest
'lookout post' is the definition.
(I've seen this before)
'boasts sent off' is the wordplay.
'boasts' becomes 'crows' (crowing is a kind of boasting).
'off' indicates anagramming the letters.
'sent' with letters rearranged gives 'nest'.
'crows'+'nest'='CROWS-NEST'
'to' is the link.
(Other definitions for crows-nest that I've seen before include "Ship's lookout point" , "Lookout platform high on ship's mast (4'1, 4)" , "Ship lookout's position" , "Masthead lookout" , "Look-out platform on sailing ship, or black bird's home" .)