Cor! A fantastic cricketer! An athlete! (7)
I believe the answer is:
acrobat
'an athlete' is the definition.
(acrobat is a kind of athlete)
'cor a fantastic cricketer' is the wordplay.
'fantastic' indicates anagramming the letters.
'cricketer' becomes 'bat' (I've seen this before).
'cor'+'a'='cora'
'cora' is an anagram of 'acro'.
'acro'+'bat'='ACROBAT'
(Other definitions for acrobat that I've seen before include "Athletic type" , "Athletic Circus Performer" , "performer of risky feats?" , "Boat car (anag.)" , "Agile circus performer" .)