UK genius catching it (7)
I believe the answer is:
britain
'uk' is the definition.
(synonyms)
'genius catching it' is the wordplay.
'genius' becomes 'brain' (synonyms).
'catching' is an insertion indicator.
'brain' enclosing 'it' is 'BRITAIN'.
(Other definitions for britain that I've seen before include "Monarchy" , "See 10" , "England, Scotland, Wales and Northern Ireland" , "Main UK island" , "State" .)