Cheer hot tennis player with shaved head (6)
I believe the answer is:
hurray
'cheer' is the definition.
(thesaurus)
'hot tennis player with shaved head' is the wordplay.
'hot' becomes 'h'.
'tennis player' becomes 'murray' (Andy Murray).
'with shaved head' means to remove the first letter.
'murray' with its first letter taken off is 'urray'.
'h'+'urray'='HURRAY'
(Other definitions for hurray that I've seen before include "very brief message of joy" , "Yippee!" , "cheer" .)