Sporting enemy is one living in Arabian peninsula (6)
I believe the answer is:
yemeni
'living in arabian peninsula' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'sporting enemy is one' is the wordplay.
'sporting' is an anagram indicator.
'is one' becomes 'i' ('i' can be a synonym of 'one').
'enemy' with letters rearranged gives 'yemen'.
'yemen'+'i'='YEMENI'
Can you help me to learn more?
(Other definitions for yemeni that I've seen before include "from an Arab country" , "Someone from Aden?" , "Person from Sana'a, say" , "Arab national" , "language" .)