Russian agreement before exercises in ruined capital (8)
I believe the answer is:
budapest
'capital' is the definition.
(capital of Hungary)
'russian agreement before exercises in ruined' is the wordplay.
'russian agreement' becomes 'da'.
'before' is a charade indicator (letters next to each other).
'exercises' becomes 'pe' (Physical Education class).
'in' means one lot of letters goes inside another.
'ruined' becomes 'bust' (I've seen this before).
'da'+'pe'='dape'
'dape' going within 'bust' is 'BUDAPEST'.
(Other definitions for budapest that I've seen before include "Hungarian capital" , "Capital of Hungary" , "Ernest Laszlo's birthplace" , "Capital city on the Danube" , "Put beads in the European city" .)