Most wary actors in play concealing gripes, oddly (7)
I believe the answer is:
cagiest
'most wary' is the definition.
('cagy' can be a synonym of 'wary')
'actors in play concealing gripes oddly' is the wordplay.
'actors in play' becomes 'cast' (I've seen this before).
'concealing' indicates putting letters inside.
'oddly' means one should take alternating letters (letters in odd-numbered positions).
The alternating letters of 'gripes' are 'gie'.
'cast' placed around 'gie' is 'CAGIEST'.
(Another definition for cagiest that I've seen is " Most cautious about giving information".)