Capital Radio host interrupting call upset one (8)
I believe the answer is:
ndjamena
'capital' is the definition.
(capital of Chad)
'radio host interrupting call upset one' is the wordplay.
'radio host' becomes 'dj'.
'interrupting' indicates putting letters inside.
'call' becomes 'name' (as in calling or naming someone something).
'upset' is a reversal indicator.
'one' becomes 'an' (an apple is one apple).
'an' backwards is 'na'.
'dj' going inside 'name' is 'ndjame'.
'ndjame'+'na'='NDJAMENA'
(Other definitions for ndjamena that I've seen before include "African capital" , "Amend Jan to the capital city of Chad" .)