It spreads cold vegetable over game (9)
I believe the answer is:
contagion
'it spreads' is the definition.
(as in a contagious disease)
'cold vegetable over game' is the wordplay.
'cold' becomes 'c' (eg on taps).
'vegetable' becomes 'onion' (onion is a vegetable).
'over' is an insertion indicator.
'game' becomes 'tag' (children's playground game).
'onion' going around 'tag' is 'ontagion'.
'c'+'ontagion'='CONTAGION'
(Other definitions for contagion that I've seen before include "Cognation (anag.)" , "cause of widespread ill-feeling" , "Communication of disease by close contact" , "Infection" .)