Players initially aware of playing a game (7)
I believe the answer is:
pontoon
'a game' is the definition.
(I've seen this before)
'players initially aware of playing' is the wordplay.
'initially' suggests taking the first letters.
'aware of' becomes 'onto' (if you're onto someone you know what they're up to).
'playing' becomes 'on' (on can mean playing or performing).
The first letter of 'players' is 'p'.
'p'+'onto'+'on'='PONTOON'
(Other definitions for pontoon that I've seen before include "Gambling game" , "Floating bridge support" , "Bridge of boats" , "'Flat-bottomed boat, card game and Mayo town (7)'" , "Card game - type of bridge" .)