Boy's found in unoccupied campus playing game (5)

I believe the answer is:

chess

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'game' is the definition.
(board game)

'boy's found in unoccupied campus playing' is the wordplay.
'boy' becomes 'Che'.
'found in unoccupied campus playing' becomes 'ss' (I can't explain this - if you can you should give a lot more credence to this answer).
'che'+'ss'='CHESS'

Can you help me to learn more?

(Other definitions for chess that I've seen before include "Board game of 13, 16 and 21" , "show" , "This is played on board" , "board meeting" , "Pure-skill board game" .)

I've seen this clue in The Irish Times.

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