Old communist way to usurp one in capital (6)
I believe the answer is:
castro
'one in capital' is the definition.
The definition suggests a singular noun which matches the answer.
'old communist way to usurp' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is located in the answer.
'way' could be 'st' (abbreviation for street) and 'st' is found within the answer.
The remaining letters 'car' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for castro that I've seen before include "Cuban leader, d. 2016" , "Latin American dictator" , "Cuban president (past and present)" , "Man of Cuba" , "Fidel -, former Cuban leader" .)