Figure a girl is a cross-country runner (5)
I believe the answer is:
volga
'cross-country runner' is the definition.
'Volga' can be an answer for 'runner' (Volga is an example). I am not certain of the 'cross-country' bit.
'figure a girl' is the wordplay.
'figure' becomes 'v' (I am not sure about this - if you are sure you should believe this answer much more).
'a girl' becomes 'Olga'.
'v'+'olga'='VOLGA'
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for volga that I've seen before include "Russian river, the longest in Europe" , "Long Russian river" , "Major River in Russia" , "River at Astrakhan" , "River flowing into the Caspian Sea" .)