Make bombs to defend old game (8)
I believe the answer is:
dominoes
'game' is the definition.
(dominoes is a kind of game)
'make bombs to defend old' is the wordplay.
'make' becomes 'do' (doing is a kind of making).
'bombs' becomes 'mines' (type of explosive device).
'to defend' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'mines' placed around 'o' is 'minoes'.
'do'+'minoes'='DOMINOES'
(Other definitions for dominoes that I've seen before include "Traditional pub game" , "Number-matching game" , "masks" , "Table-top game" , "Mistakes" .)