Man on board in hock (4)
I believe the answer is:
pawn
I believe this is a double definition.
'man on board' is the first definition.
(chess)
'hock' is the second definition.
('pawn' can be a synonym of 'hock')
'in' acts as a link.
(Other definitions for pawn that I've seen before include "Lend uncle" , "Deposit as security for a loan" , "man on board" , "Chess piece -- puppet" , "Hock; cat's-paw" .)