Leader of Opposition leaves district over in African state (5)
I believe the answer is:
niger
'african state' is the definition.
(country in Africa)
I don't understand how the remainder of the clue works.
(Other definitions for niger that I've seen before include "22 across (anag) -- northwest African river" , "The black" , "West African river and country" , "African country dominated by the Sahara, until 1969 a French colony" , "Country W. of Chad" .)