Tennis champ has broken serve finally (4)
I believe the answer is:
ashe
'tennis champ' is the definition.
(I've seen this before)
'has broken serve finally' is the wordplay.
'broken' indicates an anagram.
'finally' indicates one should take the final letters.
The last letter of 'serve' is 'e'.
'has' with letters rearranged gives 'ash'.
'ash'+'e'='ASHE'
(Other definitions for ashe that I've seen before include "US tennis player Arthur, 1975 Wimbledon champion" , "Sporting champion once" , "US rallying champion" , "He was good enough to win Wimbledon" , "Arthur, who came to court" .)