Flower on end of tennis racket (4)
I believe the answer is:
scam
'racket' is the definition.
(racket is a type of scam or scheme)
'flower on end of tennis' is the wordplay.
'flower' becomes 'cam' (river in Cambridge, England).
'on' is a charade indicator (letters next to each other).
'end of' suggests the final letters.
The last letter of 'tennis' is 's'.
'cam' put after 's' is 'SCAM'.
(Other definitions for scam that I've seen before include "Fraudulent business scheme" , "fiddle" , "Rip-off" , "A modern kind of swindle" , "Swindle, fraud (colloq.)" .)