Regularly, man's captured by pieces in chess game (4,2,3,6)
I believe the answer is:
king of the castle
'game' is the definition.
(I've seen this before)
'regularly man's captured by pieces in chess' is the wordplay.
'regularly' becomes 'oft' (often).
'man' becomes 'he' (he refers to a man).
'captured by' indicates putting letters inside.
'pieces in chess' becomes 'king castle' (two chess pieces).
'oft'+'he'='ofthe'
'ofthe' inserted within 'kingcastle' is 'KING OF THE CASTLE'.
(Other definitions for king of the castle that I've seen before include "honcho" , "Most important person in group" , "move sideways in game" , "Chessman" .)