After crucial changes, runs round (8)
I believe the answer is:
circular
'round' is the definition.
('circular' can be a synonym of 'round')
'after crucial changes runs' is the wordplay.
'after' means one lot of letters go next to another.
'changes' is an anagram indicator.
'runs' becomes 'r' (cricket abbreviation).
'crucial' is an anagram of 'circula'.
'circula'+'r' is 'CIRCULAR'.
(Other definitions for circular that I've seen before include "such unconvincing reasoning" , "Ring-shaped" , "Leaflet for mass distribution" , "plug, perhaps" , "Spherical" .)