Chessman in defensive situation (6)
I believe the answer is:
castle
This clue is a double definition.
'chessman' is the first definition.
(castle is a kind of chessman)
'defensive situation' is the second definition.
(building situated where it can be well-defended)
'in' acts as a link.
(Other definitions for castle that I've seen before include "Chess piece and fortified building" , "''An Englishman's home is his . . .''" , "making a move" , "Stately home in Yorkshire" , "Large building; rook" .)