The late developing sportsman? (7)
I believe the answer is:
athlete
'sportsman?' is the definition.
(sportsman is a kind of athlete)
'the late developing' is the wordplay.
'developing' indicates an anagram.
'the'+'late'='thelate'
'thelate' anagrammed gives 'ATHLETE'.
(Other definitions for athlete that I've seen before include "Person trained to compete in sports" , "Sporting person" , "Jumper, say" , "Runner, jumper, thrower" , "One may run" .)