Start out with a new game plan (9)
I believe the answer is:
stratagem
'plan' is the definition.
(stratagem is a kind of plan)
'start out with a new game' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'with' is a charade indicator (letters next to each other).
'a new' indicates an anagram.
'start' is an anagram of 'strat'.
'game' anagrammed gives 'agem'.
'strat'+'agem'='STRATAGEM'
(Other definitions for stratagem that I've seen before include "Ruse" , "Plan to deceive enemy" , "Crafty manoeuvre" , "Tactic to gain an advantage" , "Device" .)