Depict celebration as a game (9)
I believe the answer is:
paintball
'a game' is the definition.
(I've seen this before)
'depict celebration' is the wordplay.
'depict' becomes 'paint' (I've seen this in another clue).
'celebration' becomes 'ball' (I am not sure about this - if you are sure you should believe this answer much more).
'paint'+'ball'='PAINTBALL'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for paintball that I've seen before include "messy game" , "simulated combat" , "war game" , "Missile used in war games" .)