Sports champion remains after burning energy (4)
I believe the answer is:
ashe
'sports champion' is the definition.
(tennis player Arthur Ashe)
'remains after burning energy' is the wordplay.
'remains after burning' becomes 'ash' (remains of a fire).
'energy' becomes 'e' (physics symbol as in E=mcs).
'ash'+'e'='ASHE'
(Other definitions for ashe that I've seen before include "US tennis player Arthur, 1975 Wimbledon champion" , "Arthur ___, American tennis player 1943-1993" , "Sporting champion once" , "Arthur, first black Wimbledon men's singles champion, 1975" , "US rallying champion" .)