Puzzle resolved in game (6)
I believe the answer is:
enigma
'puzzle' is the definition.
(I've seen this in another clue)
'resolved in game' is the wordplay.
'resolved' indicates anagramming the letters.
'in'+'game'='ingame'
'ingame' with letters rearranged gives 'ENIGMA'.
(Other definitions for enigma that I've seen before include "Difficult problem" , "It's mysterious like gamine" , "Solution to mystery" , "Puzzle found in gem, Ian" , "Conundrum" .)