Looking smart, are almost all in (7)
I believe the answer is:
Here is my best explanation:
'looking' is the definition.
(staring is a kind of looking)
'smart are almost all in' is the wordplay.
'smart' becomes 'sting' (stinging is a kind of smarting**).
'almost all' means to remove the last letter.
'in' indicates putting letters inside.
'are' with its final letter taken away is 'ar'.
'sting' placed around 'ar' is 'STARING'.
(Other definitions for staring that I've seen before include "Gawking", "Looking with fixed gaze", "with eyes popping out", "Gazing long and fixedly at", "Looking fixedly" and "See 11".)