One getting into cross-country (5)
I believe the answer is:
Here is my best explanation:
'country' is the definition.
(Spain is an example)
'one getting into cross' is the subsidiary indication.
'one' becomes 'i' (roman numeral).
'getting into' means one lot of letters goes inside another.
'cross' becomes 'span' ('span' can be a synonym of 'cross'**).
'i' going within 'span' is 'spain'.
(Other definitions for spain that I've seen before include "ditto", "Ditto", "Pains badly to be in the country", "Madrid is its capital", "European country", "It pains one to be out in this country", "European monarchy", "Take pains to go there", "It pains badly when in the country" and "Iberian 4".)