Expressionless, criticise after late start (7)
I believe the answer is:
deadpan
'expressionless' is the definition.
(I know that expressionless can be written as deadpan)
'criticise after late start' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'after' says to put letters next to each other.
'late start' becomes 'dead' (I can't justify this - if you can you should believe this answer much more).
'pan' after 'dead' is 'DEADPAN'.
Can you help me to learn more?
(Other definitions for deadpan that I've seen before include "with emotionless face" , "Dry" , "without a flicker" , "Blank" , "Keeping a straight face" .)