Strikes; criticises (6)
I believe the answer is:
knocks
This clue is a double definition.
'strikes' is the first definition.
(knocking is a kind of striking)
'criticises' is the second definition.
(I know this)
(Other definitions for knocks that I've seen before include "You get bad experiences in the school of hard ..." , "Bangs on door" , "Hits" , "Reversals" , "Strikes with a sharp blow or finds fault with" .)