Cross Russia's capital, carried by driver (6)
I believe the answer is:
crabby
'cross' is the definition.
(synonyms)
'russia's capital carried by driver' is the wordplay.
'russia's capital' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'carried by' is an insertion indicator.
'driver' becomes 'cabby' (cabby is a kind of driver).
'r' placed inside 'cabby' is 'CRABBY'.
Can you help me to learn more?
(Other definitions for crabby that I've seen before include "Irritable - like a crustacean?" , "like a hermit?" , "Ill-natured" , "Cantankerous like crustacean" , "Bad-tempered, grouchy" .)