Game not played a great deal (7)
I believe the answer is:
megaton
'a great deal' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'game not played' is the wordplay.
'played' indicates anagramming the letters (letters playing around).
'game'+'not'='gamenot'
'gamenot' anagrammed gives 'MEGATON'.
Can you help me to learn more?
(Other definitions for megaton that I've seen before include "Measure of explosive power - montage (anag)" , "weight" , "it weighs a lot" , "Powerful explosive unit" , "Explosive power equivalent to one million tons of TNT" .)