Playing pieces German forces Earl to put in box (5,3)
I believe the answer is:
chess set
'playing pieces' is the definition.
'german forces earl to put in box' is the wordplay.
'german forces' becomes 'ss' (abbreviation for Schutzstaffel).
'earl' becomes 'e'.
'to put in' is an insertion indicator.
'box' becomes 'chest' (chest is a kind of box**).
'ss'+'e'='sse'
'sse' going inside 'chest' is 'CHESS SET'.
(Other definitions for chess set that I've seen before include "men, along with the board" , "King, pawns etc." , "It's played with kings, queens and bishops" , "It's played on a chequered board with 32 pieces" , "Game with kings, queens and bishops" .)