Puzzle solved in game (6)
I believe the answer is:
enigma
'puzzle' is the definition.
(I've seen this before)
'solved in game' is the wordplay.
'solved' is an anagram indicator (the anagram must be solved).
'in'+'game'='ingame'
'ingame' is an anagram of 'ENIGMA'.
(Other definitions for enigma that I've seen before include "Elgar Variations nickname" , "Riddle - German coding machine" , "It's mysterious like gamine" , "closed book" , "Title of Elgar's set of variations" .)