Working late with the jumper, say (7)
I believe the answer is:
athlete
'jumper say' is the definition.
(I know that jumper is a type of athlete)
'working late with the' is the wordplay.
'working' indicates an anagram.
'with' is a charade indicator (letters next to each other).
'late' after 'the' is 'thelate'.
'thelate' with letters rearranged gives 'ATHLETE'.
(Other definitions for athlete that I've seen before include "front-runner, possibly" , "Track performer" , "eg Dean Macey" , "Person trained to compete in sports" , "One competes in sports" .)