Country's flag reflected on side of arena (7)
I believe the answer is:
eritrea
'country's' is the definition.
(I've seen this before)
'flag reflected on side of arena' is the wordplay.
'flag' becomes 'tire' (both can mean to become weary).
'reflected' says the letters should be written in reverse (letters reflected back).
'on' becomes 're' ('on' can be mean 'with reference to').
'side of' suggests taking the first letters (the letter from one side of the word).
The first letter of 'arena' is 'a'.
'tire' in reverse letter order is 'erit'.
'erit'+'re'+'a'='ERITREA'
(Other definitions for eritrea that I've seen before include "NE African country" , "Asmara area" , "It declared its independence from Ethiopia in 1993" , "It achieved independence from Ethiopia in 1993" , "Country to the north of Ethiopia" .)