She joined a half-back in the old country (5)
I believe the answer is:
sheba
'the old country' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I can't see?
'she joined a half-back' is the wordplay.
'joined a half back' becomes 'ba' (I can't justify this - if you can you should believe this answer much more).
'she'+'ba'='SHEBA'
'in' is the link.
Can you help me to learn more?
(Other definitions for sheba that I've seen before include "Biblical Queen of . . . . . visited King Solomon" , "Ancient people of Yemen, Sabaeans" , "Old Testament realm of queen visiting Solomon" , "Solomon's guest" , "Biblical queen's realm" .)